Optical reproducing device and optical memory medium

ABSTRACT

An optical reproducing device according to the present invention detects mean amplitude values of short marks and long marks, which are recorded marks for reproducing power control, by means of a short mark level detecting circuit and a long mark level detecting circuit. Then a differential amplifier compares a ratio between these two mean amplitude values with a standard value, and outputs the result of this comparison. Thereafter, a reproducing power control circuit controls reproducing power of a semiconductor laser such that the absolute value of this comparison result is reduced. Since mean values of the amplitude values of the short marks and long marks are detected, the detection results are very accurate, and the precision of control of reproducing power can be greatly improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 09/103,869filed Jun. 24, 1998 now U.S. Pat. No. 6,288,992.

FIELD OF THE INVENTION

The present invention relates to an optical reproducing device and anoptical memory medium, and in particular to an optical reproducingdevice which controls the quantity of light of a light beam projectedonto an optical memory medium so as to bring close to a predeterminedvalue the quantity of a reproducing signal from recorded marks recordedin the optical memory medium, and to an optical memory medium to bereproduced by this optical reproducing device.

BACKGROUND OF THE INVENTION

In magneto-optical disk devices which use the magnetic ultra highresolution method, a magneto-optical disk is used which is provided witha recording layer and with a reproducing layer having in-planemagnetization. In this type of magneto-optical disk device, duringreproducing, a light beam is projected onto the reproducing layer sideof the magneto-optical disk. Then, part of the area of the reproducinglayer within the light beam spot is heated to above a predeterminedtemperature, and the magnetization of this portion (the aperture) shiftsfrom in-plane magnetization to a perpendicular magnetization conformingto that of the recording layer beneath the aperture, i.e., themagnetization of the recording layer is copied to the reproducing layer.In this way, with this type of magneto-optical disk device, byreproducing the magnetization of the aperture, recorded marks smaller indiameter than the light beam spot can be reproduced.

In magneto-optical disk devices using this magnetic ultra highresolution method, it is preferable if the power of the light beamduring reproducing (the reproducing power) is always at an optimumlevel. However, there are cases in which the optimum level of thereproducing power fluctuates with changes in the ambient temperature atthe time of reproducing. For this reason, even if the current fordriving the structure which produces the light beam (the drivingcurrent) is held constant, there are cases in which the reproducingpower deviates from the optimum level.

If reproducing power is much stronger than the optimum level, theaperture formed on the magneto-optical disk becomes too large.Consequently, output of reproducing signals from tracks adjacent to thetrack being reproduced (crosstalk) is increased, the proportion of noisesignals included in the reproduced data increases, and reading errorsare more likely to occur.

Again, if reproducing power is much weaker than the optimum level, theaperture becomes smaller than the recorded mark, and the reproducingsignal output from the target track is reduced. Accordingly, readingerrors are more likely to occur in this case as well.

In a recording and reproducing device disclosed in Japanese UnexaminedPatent Publication No. 8-63817/1996 (U.S. Pat. No. 5,617,400), in orderto control reproducing power, long marks and short marks formed on amagneto-optical disk are reproduced. These long and short marks are twotypes of recorded marks for reproducing power control of different marklengths. In this device, reproducing power is controlled so as to bringclose to a predetermined value a ratio of the quantities of thereproducing signals from these recorded marks. By this means, in thisdevice, reproducing power is maintained at an optimum value, and thelikelihood of reading errors is reduced.

FIG. 30 is an explanatory drawing showing the general structure of thisdevice. In this device, a light beam is projected from a semiconductorlaser 108 onto a magneto-optical disk 112. Then, reflected light frommarks for reproducing power control, which include long and short marks,is converted into a reproducing signal by a photodiode 113, and thisreproducing signal is sent to an A/D (Analog/Digital) converter 115 andto a clock producing circuit 114. By means of the PLL (Phase LockedLoop) control method, the clock producing circuit 104 produces a clocksignal synchronized with the reproducing signal, and sends this clocksignal to the A/D converter 115.

Then, in accordance with the clock signal, the A/D converter 115converts the reproducing signal into digital signals, which are sent toan amplitude ratio detecting circuit 116. The amplitude ratio detectingcircuit 116 extracts, from the digital signals inputted for each clocksignal, only the digital signals corresponding to upper and lower peakpoints. Then the amplitude ratio detecting circuit 116, based on theextracted digital signals, calculates the values of these upper andlower peak points and finds amplitude values for the long and shortmarks. Then a ratio between these amplitudes (amplitude ratio) iscalculated and sent to a differential amplifier 110. This amplituderatio corresponds with the size of the aperture on the reproducing layerof the magneto-optical disk.

The differential amplifier 110 compares the amplitude ratio with apredetermined standard value, and sends the results of this comparisonto a reproducing power control circuit 111. The reproducing powercontrol circuit 111 then controls driving current supplied to thesemiconductor laser 108 in such a way that feedback reduces thedifference between the amplitude ratio and the standard value.

In this way, the driving current supplied to the semiconductor laser 108is controlled in such a manner that the light beam is always projectedonto the magneto-optical disk at optimum reproducing power.

However, with this recording and reproducing device, the amplitudevalues of the recorded marks for reproducing power control arecalculated using the values of only one upper peak point and one lowerpeak point. For this reason, the amplitude ratio calculated from theseamplitude values is not sufficiently accurate, and thus there is a largeerror in control of reproducing power in this recording and reproducingdevice.

Again, as a method of reducing reading error rate with data recorded athigh density, the PRML (Partial Response Maximum Likelihood)demodulating method has been proposed. The PRML demodulating method is ademodulating method in which a reproducing signal undergoes partialresponse equalization, and then maximum likelihood decoding (MLdecoding) using Viterbi decoding.

A reproducing device using this demodulating-method is disclosed, forexample, in Japanese Unexamined Patent Publication No. 6-243598/1994. Inthis device, a reproducing signal from an optical disk is equalized intoPR(1,2,1) characteristics, and decoded into the most likely data bymeans of Viterbi decoding. FIG. 31 is an explanatory drawing showing thegeneral structure of this device.

In reproducing using this device, an optical head 121 reads datarecorded in an optical disk 120, and outputs an analog signalcorresponding to this data. Then an A/D (Analog/Digital) converter 123converts the analog signal into digital signals. The digital signalsoutputted by the A/D converter 123 are sent to a PRML demodulatingcircuit 126.

The PRML demodulating circuit 126 includes a PR equalizer 124 and aViterbi decoder 125. The digital signals are equalized into PR(1,2,1)characteristics by the PR equalizer 124, and then Viterbi decoded by theViterbi decoder 125, which outputs binarized data.

The analog signal outputted by the optical head 121 is also sent to aclock extracting section 122. The clock extracting section 122 producesand outputs to the A/D converter 123 clock signals with a bit cyclesynchronized with the analog signal. The A/D converter 123 converts theanalog signal to digital signals in accordance with the timing of theclock signal.

However, drawbacks of this reproducing device include the following.Namely, in this reproducing device, the sampling timing which ispreferable for data reproducing, which is determined by the combinationof the modulation method of the data recorded in the optical disk 120and the demodulation method used by the PRML demodulating circuit 126,may not conform to the sampling timing which is preferable foraccurately detecting the quantity of the reproducing signal of therecorded marks for reproducing power control.

Consider reproducing power when using PR(1,2,1)ML demodulating in thePRML demodulating circuit 126 to decode data from an optical diskrecorded, for example, by the (1,7)RLL (Run Length Limited) modulationmethod.

FIG. 32 is an explanatory drawing showing, for this structure, thetiming of A/D conversion (sampling) suited to PR(1,2,1)ML demodulatingfor a reproducing signal consisting of a pattern of repeated shortestmarks (mark length 2Tc). As shown in FIG. 32, with sampling suited toPR(1,2,1)ML demodulating, a point at the shoulder of the reproducingsignal is sampled.

On the other hand, the mark length of the short marks used forreproducing power control is typically 2Tc. Further, when reproducingthese short marks, it is preferable to sample the upper and lower peakpoints of the reproducing signal obtained. However, as shown in FIG. 32,in sampling with this structure, a point at the shoulder of areproducing signal corresponding to recorded marks 2Tc in length issampled. Accordingly, it is not preferable to use the reproducing signalquantity obtained by this sampling for reproducing power control.Accordingly, a drawback of this structure is that, if A/D conversion isperformed with a timing suited to PR(1,2,1)ML demodulating, it isdifficult to perform reproducing power control.

In this example, a combination of PR(1,2,1)ML demodulating and (1,7)RLLmodulation was considered, but for data reproduced by othercombinations, too, such as PR(1,1)ML demodulating and the EFM (Eight toFourteen Modulation) modulation method, there is a sampling timingpreferable for the combination used.

In this way, conventional structures have the problem that, when theoptimum sampling timing for data reproducing (which is determined by thecombination of the PRML demodulating method and the modulation method)does not conform with the optimum sampling timing for reproducing powercontrol, accurate reproducing is difficult.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide an opticalreproducing device capable of precisely calculating the quantity of areproducing signal obtained from an optical memory medium, and, based onthe amplitude value of that reproducing signal quantity, preciselycontrolling reproducing power, and to provide an optical memory mediumto be reproduced by this optical reproducing device.

Further, the second object of the present invention is to provide anoptical reproducing device capable of performing reproducing powercontrol and digital data reproducing using optimum clock signals.

In order to attain the first object mentioned above, an opticalreproducing device according to the present invention is made up of areproducing signal production section, which projects a light beam ontoan optical memory medium, and, based on reflected light of the lightbeam, produces a reproducing signal corresponding to recorded marksrecorded in the optical memory medium; a control signal output section,which detects a mean value of a signal quantity of the reproducingsignal produced by the reproducing signal production section, andproduces a first control signal corresponding to the mean value; and areproducing power control section, which, based on the first controlsignal produced by the control signal output section, controlsreproducing power of the light beam projected by the reproducing signalproduction section such that the signal quantity of the reproducingsignal is a predetermined value.

In the foregoing structure, the reproducing signal production sectionprojects a light beam onto the optical memory medium, and produces areproducing signal corresponding to recorded marks recorded in theoptical memory medium. The quantity of this reproducing signalcorresponds with the reproducing power of the light beam projected ontothe optical memory medium.

Then the control signal output section calculates a mean value of anamplitude of the reproducing signal, and, based on this mean value,produces a first control signal. The first control signal is produced onthe basis of the mean of the amplitude value, and thus corresponds withthe quantity of the reproducing signal from the optical memory medium.

Then the reproducing power control section, based on the first controlsignal, controls the reproducing power of the light beam projected ontothe optical memory medium by the reproducing signal production section.In other words, the reproducing power control section judges thequantity of the current reproducing signal from the first controlsignal, and controls the reproducing power of the light beam projectedonto the optical memory medium by the reproducing signal productionsection in such a manner that the quantity of the reproducing signal isa predetermined value.

In this way, the foregoing structure can always maintain a reproducingpower capable of producing a reproducing signal of a predeterminedsignal quantity. Consequently, the frequency of reading errors such ascrosstalk can be reduced, and stable reproducing is enabled.

Further, in the foregoing structure, the control signal output sectiondetects a mean value of the reproducing signal quantity, and producesthe first control signal on the basis of this mean value. Accordingly,the first control signal reflects the actual value of the reproducingsignal quantity with great accuracy. Accordingly, the reproducing powercontrol section is enabled to control the reproducing power of thereproducing signal production section with great accuracy.

Incidentally, the predetermined signal quantity referred to above is,for example, the optimum signal quantity for reproducing in the presentoptical reproducing device. Further, “signal quantity” is, for example,the amplitude value of the reproducing signal.

Further, in order to attain the second object mentioned above, anotheroptical reproducing device according to the present invention is made upof a reproducing signal production section, which projects a light beamonto an optical memory medium, and, based on reflected light of thelight beam, produces a reproducing signal corresponding to recordedmarks recorded in the optical memory medium; a digital signal outputsection, which outputs digital signals corresponding to the reproducingsignal; a demodulation section, which demodulates the digital signals;and a reproducing power control section, which, based on the digitalsignals, controls reproducing power of the reproducing signal productionsection; in which the digital signal output section, is made up of aclock signal output section, which outputs a clock signal in accordancewith the modulation method of the recorded marks, the demodulationmethod of the demodulation section, and the control method of thereproducing power control section; and a digital signal producingsection, which, based on the clock signal outputted by the clock signaloutput section, samples the reproducing signal and produces digitalsignals.

In the foregoing structure, the reproducing signal production sectionprojects a light beam onto the optical memory medium, and produces areproducing signal according to recorded marks recorded in the opticalmemory medium.

Further, the digital signal output section includes a clock signaloutput section, which produces a clock signal based on the reproducingsignal. This clock signal is a clock signal which is in accordance withthe modulation method of the recorded marks, the demodulation method ofthe demodulation section, and the control method of the reproducingpower control section. Then the digital signal producing section, basedon the clock signal, produces digital signals corresponding to thereproducing signal.

Typically, the timing of sampling for production of digital signalssuitable for demodulating by a demodulation section is determined by themodulation method of the recorded marks and the demodulation method ofthe demodulation section. Further, the timing of sampling for productionof digital signals suitable for reproducing power control is determinedby the modulation method of the recorded marks and the control method ofthe reproducing power control section. In addition, the timing ofsampling is determined by a clock signal.

For these reasons, the clock signal output section, giving considerationto the foregoing modulation method, demodulation, and control method,produces a clock signal capable of producing both of the foregoingdigital signals. This clock signal may be two different clock signals,or it may be a single clock signal capable of producing both of theforegoing digital signals.

Next, the digital signal producing section, based on the clock signaloutputted by the clock signal output section, produces the digitalsignals for outputting to the demodulation section and the digitalsignals for outputting to the reproducing power control section, andoutputs these digital signals to the demodulation section and thereproducing power control section, respectively.

Accordingly, with the foregoing structure, even if the timing ofsampling for producing the digital signals for demodulation differs fromthe timing of sampling for producing the digital signals suited toreproducing power control, it is possible to perform accuratereproducing power control and demodulation with a low error rate.

Additional objects, features, and strengths of the present inventionwill be made clear by the description below. Further, the advantages ofthe present invention will be evident from the following explanation inreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory drawing showing the structure of a magneticultra high resolution optical reproducing device according to the firstembodiment of the present invention.

FIG. 2 is an explanatory drawing showing the structure of amagneto-optical disk for reproducing by the optical reproducing deviceshown in FIG. 1.

FIG. 3 is an explanatory drawing showing the structure of sectors formedin the magneto-optical disk shown in FIG. 2.

FIG. 4 is an explanatory drawing showing short marks and long marksformed in the magneto-optical disk shown in FIG. 2.

FIG. 5 is an explanatory drawing showing the structure of a short marklevel detecting circuit in the optical reproducing device shown in FIG.1.

FIG. 6 is an explanatory drawing showing the structure of a shiftregister in the short mark level detecting circuit shown in FIG. 5.

FIG. 7 is an explanatory drawing showing the structure of a long marklevel detecting circuit in the optical reproducing device shown in FIG.1.

FIG. 8 is an explanatory drawing showing the structure of a shiftregister in the long mark level detecting circuit shown in FIG. 7.

FIG. 9 is an explanatory drawing showing sampling by an A/D converter ofan analog reproducing signal obtained from a short mark recording domainof the magneto-optical disk shown in FIG. 2.

FIG. 10 is an explanatory drawing showing sampling by an A/D converterof an analog reproducing signal obtained from a long mark recordingdomain of the magneto-optical disk shown in FIG. 2.

FIG. 11 is a graph showing the results of measurement of therelationship between (i) a mean number of bytes of the magneto-opticaldisk short marks and long marks shown in FIG. 4 and (ii) precision of amean amplitude ratio detected by the optical reproducing device shown inFIG. 1.

FIG. 12 is a graph, showing the results of measurement, in the opticalreproducing device shown in FIG. 1, of the relationship between (i)reproducing power of the semiconductor laser and (ii) the BER ofbinarized data obtained from the data reproducing circuit; and of therelationship between (i) the same reproducing power and (iii) a meanamplitude ratio calculated by the division circuit.

FIG. 13 is a graph showing the results of measurement of therelationship between (i) a mean number of bytes of short marks and oflong marks in a magneto-optical disk whose modulation method is NRZImodulation and (ii) precision of a mean amplitude ratio detected by theoptical reproducing device shown in FIG. 1.

FIG. 14 is a graph showing the results of measurement, when reproducinga magneto-optical disk whose modulation method is NRZI modulation in theoptical reproducing device shown in FIG. 1, of the relationship between(i) reproducing power of the semiconductor laser and (ii) the BER ofbinarized data obtained from the data reproducing circuit; and of therelationship between (i) the same reproducing power and (iii) a meanamplitude ratio calculated by the division circuit.

FIG. 15 is an explanatory drawing showing short marks recorded by meansof (1,7)RLL modulation, and sampling of an analog reproducing signalcorresponding to these short marks.

FIG. 16 is an explanatory drawing showing long marks recorded by meansof (1,7)RLL modulation, and sampling of an analog reproducing signalcorresponding to these long marks.

FIG. 17 is an explanatory drawing showing short marks recorded by meansof NRZI modulation, and sampling of an analog reproducing signalcorresponding to these short marks.

FIG. 18 is an explanatory drawing showing long marks recorded by meansof NRZI modulation, and sampling of an analog reproducing signalcorresponding to these long marks.

FIG. 19 is an explanatory drawing showing the structure of an opticalreproducing device according to the second embodiment of the presentinvention.

FIG. 20 is an explanatory drawing showing the structure of amagneto-optical disk for reproducing by the optical reproducing deviceshown in FIG. 19.

FIG. 21 is an explanatory drawing showing the structure of sectorsformed in the magneto-optical disk shown in FIG. 20.

FIG. 22 is an explanatory drawing showing short marks and long marksformed in the magneto-optical disk shown in FIG. 20.

FIG. 23 is an explanatory drawing showing clock signals produced by afirst clock producing circuit and a second clock producing circuit inthe optical reproducing device shown in FIG. 19.

FIG. 24 is an explanatory drawing showing the relationship between theforegoing clock signals and analog reproducing signals corresponding tothe foregoing short marks and long marks, which are sampled inaccordance with the clock signals.

FIG. 25 is an explanatory drawing showing, in the optical reproducingdevice shown in FIG. 19, sampling by an A/D converter of an analogreproducing signal corresponding to short marks, and of an analogreproducing signal corresponding to long marks.

FIG. 26 is an explanatory drawing showing the structure of an opticalreproducing device according to the third embodiment of the presentinvention.

FIG. 27 is an explanatory drawing for comparing a clock signal producedby a doubled clock producing circuit in the optical reproducing deviceshown in FIG. 26 with the clock signals shown in FIG. 23.

FIG. 28 is an explanatory drawing showing production of digitalreproducing signals by an A/D converter in the optical reproducingdevice shown in FIG. 26, when an analog reproducing signal correspondingto recorded marks with a mark length of 2Tc is inputted.

FIG. 29 is an explanatory drawing showing production of digitalreproducing signals by the foregoing A/D converter, when reproducingdigital data made up of a random pattern of recorded marks of variousmark lengths.

FIG. 30 is an explanatory drawing schematically showing the structure ofa conventional optical reproducing device.

FIG. 31 is an explanatory drawing schematically showing the structure ofanother conventional optical reproducing device.

FIG. 32 is an explanatory drawing showing the timing of sampling, suitedto PR(1,2,1)ML modulation, of a reproducing signal obtained byreproducing a pattern of repeated recorded marks 2Tc in length using theoptical reproducing device shown in FIG. 31.

FIG. 33 is an explanatory drawing showing the wave-form of a reproducingsignal corresponding to recorded marks 1Tc in length.

FIG. 34 is an explanatory drawing showing the wave-form of a reproducingsignal corresponding to a pattern of repeated recorded marks 2Tc inlength.

DESCRIPTION OF THE EMBODIMENTS

[First Embodiment]

The first embodiment of the present invention will be explained below.

FIG. 1 is an explanatory drawing showing the structure of a magneticultra high resolution optical reproducing device (hereinafter referredto as “the present reproducing device”). As shown in the Figure, thepresent reproducing device is made up of an optical head 2, a clockproducing circuit 4, an A/D converter 5, a short mark level detectingcircuit 6, a long mark level detecting circuit 7, a data reproducingcircuit 8, a division circuit 9, a differential amplifier 10, areproducing power control circuit 11, and an error correcting circuit14. Further, the magneto-optical disk 1 shown in FIG. 1 is an opticalmemory medium to be reproduced by the present reproducing device.

Prior to explaining the structure of the present reproducing device, thestructure of the magneto-optical disk 1 will first be explained. In themagneto-optical disk 1 various data is recorded by (1,7)RLL (Run LengthLimited) modulation. FIG. 2 is an explanatory drawing showing thestructure of the magneto-optical disk 1. As shown in the Figure, arecording track 21 is formed in the shape of a circular band concentricwith the circular magneto-optical disk 1. Further, in the recordingtrack 21 are successively formed a plurality of sectors 22.

FIG. 3 is an explanatory drawing showing the structure of a sector 22.As shown in the Figure, in each sector 22 are formed a short markrecording domain 23, a long mark recording domain 24, and a datarecording domain 25.

The short mark recording domains 23 (reproducing power control domains)are domains in which are formed short marks, which are marks forreproducing power control. The long mark recording domains 24(reproducing power control domains) are domains in which are formed longmarks, which are also marks for reproducing power control. The datarecording domains 25 are domains in which the user's desired data,modulated by (1,7)RLL, is recorded as digital data.

FIG. 4 is an explanatory drawing showing the short marks and the longmarks, at (a) and (b), respectively. As shown in the Figure, in theshort mark recording domain 23, short marks having a mark length of 2Tc(Tc being the length of a channel bit) are successively formed at aninterval of 2Tc. In the same way, in the long mark recording domain 24,long marks having a mark length of 8Tc are successively formed at a markinterval of 8Tc. In what follows, the number of short marks and longmarks formed in the short mark recording domain 23 and the long markrecording domain 24 will be N marks and M marks, respectively (N and Mbeing predetermined natural numbers).

The following will explain each of the structures of the presentreproducing device, shown in FIG. 1.

The optical head 2 includes a semiconductor laser 12 and a photodiode13. The semiconductor laser 12 (reproducing signal production section;light beam projecting section) projects a light beam onto the recordingtrack 21 of the magneto-optical disk 1 at a predetermined reproducingpower. The photodiode 13 (reproducing signal production section; lightreceiving section) receives light reflected from each of the domains 23through 25 of the sector 22, and produces and outputs an analogreproducing signal corresponding to this reflected light.

In what follows, this analog reproducing signal obtained from themagneto-optical disk 1 will be referred to as the “analog reproducingsignal.”

The clock producing circuit 4 (control signal output section), by meansof PLL (Phase Locked Loop), produces a clock signal synchronized withthe channel bit frequency of the analog reproducing signal, and outputsthis clock signal to the A/D converter 5.

The A/D converter 5 (control signal output section; amplitude valuedetecting section) receives the analog reproducing signal and the clocksignal, samples the analog reproducing signal on the basis of the clocksignal, and produces digital signals corresponding to the value of theanalog reproducing signal at each sampling point. The A/D converter 5then sends these digital signals to the short mark level detectingcircuit 6, the long mark level detecting circuit 7, and the datareproducing circuit 8. In what follows, the digital signalscorresponding to each sampling point will be referred to as the “digitalreproducing signals.” Sampling of the analog reproducing signal by theA/D converter 5 will be discussed later.

Based on the digital reproducing signals received from the A/D converter5, the short mark level detecting circuit 6 (control signal outputsection; mean value producing section; first mean value calculatingsection) calculates a mean value of all of the maximal values of theanalog reproducing signal obtained from the entirety of a single shortmark recording domain 23, and calculates a mean value of all of theminimal values of the same analog reproducing signal. Then, on the basisof these two mean values, the short mark level detecting circuit 6calculates a mean amplitude value for the analog reproducing signalobtained from that single short mark recording domain 23 (short markmean amplitude value).

FIG. 5 is an explanatory drawing showing the structure of the short marklevel detecting circuit 6. As shown in the Figure, the short mark leveldetecting circuit 6 is made up of a shift register 31, addition circuits32 and 33, division circuits 34 and 35, and a subtraction circuit 36.

The shift register 31 is a shift register of 4N stages. FIG. 6 is anexplanatory drawing showing the structure of the shift register 31. Asshown in the Figure, the shift register 31 is made up of 4N cells,including cells ds₀ through ds_(4(N−1)+3). The shift register 31 storesthe values of the digital reproducing signals obtained from the singleshort mark recording domain 23 and sent from the A/D converter 5 foreach clock signal outputted by the clock producing circuit 4, in order,in cells ds₀ through ds_(4(N−1)+3).

The addition circuits 32 and 33 add the digital reproducing signalvalues stored in predetermined cells of the shift register 31, andoutput the total values obtained thereby. The division circuits 34 and35 divide by N the total values received from the addition circuits 32and 33, respectively, and send the respective divided values to thesubtraction circuit 36. In the subtraction circuit 36, the divided valuereceived from the division circuit 35 is subtracted from the dividedvalue received from the division circuit 34, and the resulting value issent to the division circuit 9 shown in FIG. 1.

Calculation of the short mark mean amplitude value by the short marklevel detecting circuit 6 will be discussed later.

The long mark level detecting circuit 7 (control signal output section;mean value producing section; second mean value calculating section),based on the digital reproducing signals received from the A/D converter5, calculates a mean value of all of the maximal values of the analogreproducing signal obtained from the entirety of a single long markrecording domain 24, and calculates a mean value of all of the minimalvalues of the same analog reproducing signal. Then, on the basis ofthese two mean values, the long mark level detecting circuit 7calculates a mean amplitude value for the analog reproducing signalobtained from that single long mark recording domain 24 (long mark meanamplitude value).

FIG. 7 is an explanatory drawing showing the structure of the long marklevel detecting circuit 7. As shown in the Figure, the long mark leveldetecting circuit 7 is made up of a shift register 41, addition circuits42 and 43, division circuits 44 and 45, and a subtraction circuit 46.

The shift register 41 is a shift register of 16M stages. FIG. 8 is anexplanatory drawing showing the structure of the shift register 41. Asshown in the Figure, the shift register 41 is made up of 16M cells,including cells dl₀ through dl_(16(M−1)+15). The shift register 41stores the values of the digital reproducing signals obtained from thesingle long mark recording domain 24 and sent from the A/D converter 5for each clock signal outputted by the clock producing circuit 4, inorder, in cells dl₀ through dl_(16(M−1)+15).

The addition circuits 42 and 43 add the digital reproducing signalvalues stored in predetermined cells of the shift register 41, andoutput the total values obtained thereby. The division circuits 44 and45 divide by 4M the total values received from the addition circuits 42and 43, respectively, and send the respective divided values to thesubtraction circuit 46. In the subtraction circuit 46, the divided valuereceived from the division circuit 45 is subtracted from the dividedvalue received from the division circuit 44, and the resulting value issent to the division circuit 9 shown in FIG. 1.

Calculation of the long mark mean amplitude value by the long mark leveldetecting circuit 7 will be discussed later.

The data reproducing circuit 8 (binarized data producing section)detects the level of, among the digital reproducing signals receivedfrom the A/D converter 5, the signal obtained from the light reflectedfrom the data recording domain 25. In other words, the data reproducingcircuit 8 produces binarized data corresponding to, among the digitalreproducing signals received from the A/D converter 5, the signalobtained from the data recording domain 25.

The division circuit 9 (control signal output section; control signalproducing section) receives the short mark mean amplitude value and thelong mark mean amplitude value sent from the short mark level detectingcircuit 6 and the long mark level detecting circuit 7, respectively, andcalculates an outputs a ratio between these two mean amplitude values(mean amplitude ratio; first control signal).

The differential amplifier 10 (reproducing power control section)compares the mean amplitude ratio received from the division circuit 9with a standard value received from a standard value producingcircuit(not shown), and outputs the result of this comparison (thedifference of the mean amplitude ratio and the standard value; secondcontrol signal). The mean amplitude ratio is in accordance with thesignal quantity of the analog reproducing signal, i.e., with the size ofthe aperture in the reproducing layer of the magneto-optical disk 1.

The standard value is, for example, the value of a mean amplitude ratiodetected when the present reproducing device performs reproducing at areproducing power with which the bit error rate is minimized, i.e., theoptimum reproducing power. Alternatively, the standard value may be amedian value of a preferable range for the mean amplitude ratio. In thepresent reproducing device, a standard value of this kind is measured inadvance, and stored in a memory device (not shown).

The reproducing power control circuit 11 (reproducing power controlsection; reproducing power adjusting section) supplies driving currentto the semiconductor laser 12, and, by controlling the amperage of thedriving current, controls the reproducing power of the semiconductorlaser 12. The reproducing power control circuit 11 receives the resultof comparison from the differential amplifier 10, and controls thedriving current supplied to the semiconductor laser 12 so as to reducethe absolute value of this comparison result.

The error correcting circuit 14 (error correcting section) is a circuitfor correcting errors in the binarized data outputted by the datareproducing circuit 8. The error correcting circuit 14 is capable ofcorrecting errors in the binarized data with certainty when the biterror rate (BER) thereof is 1E-4 (1×10⁻⁴) or less.

The following will explain the operations of the present reproducingdevice when reproducing the magneto-optical disk 1.

During reproducing, reproducing begins with the short mark recordingdomain 23 of the sector 22. In other words, the light beam projected bythe semiconductor laser 12 is first projected, at a predeterminedinitial reproducing power, onto the short mark recording domain 23. Thisinitial reproducing power is as follows. When the reproducing powercontrol circuit 11 is not receiving a feedback signal from thedifferential amplifier 10, the reproducing power control circuit 11supplies a previously set initial driving current to the semiconductorlaser 12. In other words, the initial reproducing power of thesemiconductor laser 12 is a reproducing power obtained in accordancewith the initial driving current.

Light reflected from the short mark recording domain 23 is received bythe photodiode 13, which produces an analog reproducing signal, which issent to the clock producing circuit 4 and the A/D converter 5. The clockproducing circuit 5 produces and outputs to the A/D converter 5 a clocksignal synchronized with the channel bit frequency of the analogreproducing signal.

In accordance with the timing of the clock signal outputted by the clockproducing circuit 4, the A/D converter 5 produces digital reproducingsignals from the analog reproducing signal, and outputs the digitalreproducing signals to the short mark level detecting circuit 6. FIG. 9is an explanatory drawing showing sampling by the A/D converter 5 of ananalog reproducing signal obtained from the short mark recording domain23. In the Figure, sampling points are indicated by “∘.”

As shown in FIG. 9, the sampling points sampled by the A/D converter 5are of four types: an upper peak of the analog reproducing signal, alower peak, and two points intermediate between these peaks. In whatfollows, as shown in the Figure, the upper peak point of the analogreproducing signal will be indicated as sampling point s_(4i), theintermediate point passed when traveling from the upper peak point tothe lower peak point as sampling point s_(4i+1), the lower peak point assampling point s_(4i+2), and the intermediate point passed whentraveling from the lower peak point to the upper peak point as samplingpoint s_(4i+3). Here, i=0, 1, . . . , N−1.

The A/D converter 5 converts the value of the analog reproducing signalat each of these sampling points to a digital reproducing signal, andsuccessively outputs each of these digital reproducing signals. In otherwords, for every four sampling points, an upper peak point, a lower peakpoint, and two intermediate points of the analog reproducing signal areoutputted.

Upon receiving the digital reproducing signals outputted by the A/Dconverter 5, the short mark level detecting circuit 6 stores thesedigital reproducing signals in the shift register 31 as follows. Namely,digital reproducing signals for the sampling points s₀ throughs_(4(N−1)+3) are stored in order in the cells ds₀ through ds_(4(N−1)+3),4N in number, of the shift register 31 (shown in FIG. 6). In otherwords, the digital reproducing signals for the sampling points s_(4i),s_(4i+1), s_(4i+2), and s_(4i+3) (i=0, 1, . . . , (N−1)) are stored inthe cells ds_(4i), ds_(4i+1), ds_(4i+2), and ds_(4i+3), respectively.The digital reproducing signal stored in each cell is held untilreproducing of the short mark recording domain 23 is completed.

When reproducing of the short mark recording domain 23 is complete, theshift register 31 sends all of the digital reproducing signal values forthe sampling points s_(4i) (which are stored in the cells ds_(4i)),i.e., the values of the upper peak points of the analog reproducingsignal, to the addition circuit 32. Again, the shift register 31 sendsall of the digital reproducing signal values for the sampling pointss_(4i+2) (which are stored in the cells ds_(4i+2)), i.e., the values ofthe lower peak points of the analog reproducing signal, to the additioncircuit 33.

The addition circuit 32 adds all of the digital reproducing signalvalues for the sampling points s_(4i), and sends the total obtained tothe division circuit 34. Again, the addition circuit 33 adds all of thedigital reproducing signal values for the sampling points s_(4i+2), andsends the total obtained to the division circuit 35.

The division circuit 34 divides the value received from the additioncircuit 32 by N, thus obtaining a mean value for the sampling pointss_(4i), which are the upper peak points of the analog reproducingsignal. In what follows, the mean value of the sampling points s_(4i)will be referred to as “Ts_(mean).” Again, the division circuit 35divides the value received from the addition circuit 33 by N, thusobtaining a mean value for the sampling points s_(4i+2), which are thelower peak points of the analog reproducing signal. In what follows, themean value of the sampling points s_(4i+2) will be referred to as“Bs_(mean).” Next, the division circuits 34 and 35 send Ts_(mean) andBs_(mean) to the subtraction circuit 36. The subtraction circuit 36subtracts Bs_(mean) from Ts_(mean), thus obtaining a mean amplitudevalue for the short marks, and outputs this value to the divisioncircuit 9. In other words, the subtraction circuit 36 calculates(Ts_(mean)−Bs_(mean)), and outputs this value to the division circuit 9as the short mark mean amplitude value.

After reproducing of the short mark recording domain 23, the light beam,still projected by the semiconductor laser 12 at the predeterminedinitial reproducing power, is projected onto the long mark recordingdomain 24. Then, as with reproducing of the short mark recording domain23, an analog reproducing signal is sent to the A/D converter 5. Thenthe A/D converter 5, in accordance with the timing of the clock signaloutputted by the clock producing circuit 4, produces digital reproducingsignals from the analog reproducing signal, and outputs the digitalreproducing signals to the long mark level detecting circuit 7.

FIG. 10 is an explanatory drawing showing sampling by the A/D converter5 of an analog reproducing signal obtained from the long mark recordingdomain 24. In the Figure, sampling points are indicated by “∘.”

As shown in FIG. 10, the A/D converter 5 samples each cycle of theanalog reproducing signal at 16 points. In what follows, as shown in theFigure, the four upper envelope points of the analog reproducing signalwill be indicated as sampling points l_(16j), l_(16j+1), l_(16j+2), andl_(16j+3); the four lower envelope points as l_(16j+8), l_(16j+9),l_(16j+10), and l_(16j+11); the four intermediate points passed whentraveling from the upper envelope to the lower envelope as samplingpoints l_(16j+4), l_(16j+5), l_(16j+6), and l_(16j+7); and the fourintermediate points passed when traveling from the lower envelope to theupper envelope as sampling points l_(16j+12), l_(16j+13), l_(16j+14),and l_(16j+15). Here, j=0, 1, . . . , M−1. The A/D converter 5 convertsthe value of the analog reproducing signal at each of these samplingpoints to a digital reproducing signal, and successively outputs each ofthese digital reproducing signals.

When it receives the digital reproducing signals outputted by the A/Dconverter 5, the long mark level detecting circuit 7 stores thesedigital reproducing signals in the shift register 41 as follows. Namely,digital reproducing signals for the sampling points l₀ throughl_(16(M−1)+1) are stored in order in the cells dl₀throughdl_(16(M−1)+1), 16M in number, of the shift register 41 (shown in FIG.8). In other words, the digital reproducing signals for the samplingpoints l_(16j) through l_(16j+15) (j=0, 1, . . . , (M−1)) are stored inthe cells dl_(16j) through dl_(16j+15), respectively. The digitalreproducing signal stored in each cell is held until reproducing of thelong mark recording domain 24 is completed.

When reproducing of the long mark recording domain 24 is complete, theshift register 41 sends all of the digital reproducing signal values forthe sampling points l_(16j) through l_(16j+3) (which are stored in thecells dl_(16j) through dl_(16j+3)), i.e., the values of the upperenvelope points of the analog reproducing signal, to the additioncircuit 42. Again, the shift register 41 sends all of the digitalreproducing signal values for the sampling points l_(16j+8) throughl_(16j+11) (which are stored in the cells dl_(16j+8) throughdl_(16j+11)), i.e., the values of the lower envelope points of theanalog reproducing signal, to the addition circuit 43.

The addition circuit 42 adds all of the digital reproducing signalvalues for the sampling points l_(16j) through l_(16j+3), and sends thetotal obtained to the division circuit 44. Again, the addition circuit43 adds all of the digital reproducing signal values for the samplingpoints l_(16j+8) through l_(16j+11), and sends the total obtained to thedivision circuit 45.

The division circuit 44 divides the value received from the additioncircuit 42 by 4M, thus obtaining a mean value for the sampling pointsl_(16j) through l_(16j+3), which are the upper envelope points of theanalog reproducing signal. In what follows, the mean value of thesampling points l_(16j) through l_(16j+3) will be referred to as“Tl_(mean).” Again, the division circuit 45 divides the value receivedfrom the addition circuit 43 by 4M, thus obtaining a mean value for thesampling points l_(16j+8) through l_(16j+11), which are the lowerenvelope points of the analog reproducing signal. In what follows, themean value of the sampling points l_(16j+8) through l_(16j+11) will bereferred to as “Bl_(mean).” Next, the division circuits 44 and 45 sendTl_(mean) and Bl_(mean) to the subtraction circuit 46. The subtractioncircuit 46 subtracts Bl_(mean) from Tl_(mean), thus obtaining a meanamplitude value for the long marks, and outputs this value to thedivision circuit 9. In other words, the subtraction circuit 46calculates (Tl_(mean)−Bl_(mean)), and outputs this value to the divisioncircuit 9 as the long mark mean amplitude value.

After receiving the short mark mean amplitude value and the long markmean amplitude value, the division circuit 9 calculates and outputs tothe differential amplifier 10 a mean amplitude ratio, which is a ratiobetween the two mean amplitude values. In other words, the divisioncircuit 9 calculates (Ts_(mean)−Bs_(mean))/(Tl_(mean)−Bl_(mean)), andoutputs this value to the differential amplifier 10 as the meanamplitude ratio.

The differential amplifier 10 compares the mean amplitude ratio receivedfrom the division circuit 9 with a standard value, and outputs theresult of this comparison to the reproducing power control circuit 11.Then the reproducing power control circuit 11 controls the drivingcurrent of the semiconductor laser 12 in such a way that feedbackreduces the value of the comparison result. By this means, thesemiconductor laser 12 projects the light beam at an optimum reproducingpower.

After reproducing of the long mark recording domain 24, the light beam,now projected by the semiconductor laser 12 at an optimum reproducingpower, is projected onto the data recording domain 25. Then, as withreproducing of the short mark recording domain 23 and the long markrecording domain 24, an analog reproducing signal corresponding to thedigital data of the data recording domain 25 is sent to the A/Dconverter 5.

The A/D converter 5 performs a predetermined A/D conversion of theanalog reproducing signal, thus producing digital reproducing signals,which are sent to the data reproducing circuit 8. The data reproducingcircuit 8 produces binarized data based on the digital reproducingsignals, and sends the binarized data to the error correcting circuit14. The error correcting circuit 14 corrects errors in the binarizeddata, and sends it to a binarized data processing device (not shown).Thereafter, on the basis of the binarized data, informationcorresponding to the digital data is reproduced.

When reproducing of the data recording domain 25 is completed, thuscompleting reproducing of a single sector 22, another sector 22 adjacentthereto is reproduced in the same way. In reproducing this subsequentsector 22, too, the driving current supplied to the semiconductor laser12 is first controlled so that the reproducing power thereof is optimum,and then the data recording domain 25 is reproduced.

As discussed above, in the present reproducing device, in order tocalculate amplitude values for the short marks and long marks, analogreproducing signals corresponding to a predetermined number of shortmarks and long marks are sampled, and a short mark mean amplitude valueand a long mark mean amplitude value are calculated. Then, a ratiobetween the short mark mean amplitude value and the long mark meanamplitude value, i.e., a mean amplitude ratio, is calculated, andreproducing power control is performed on the basis of this meanamplitude ratio.

By this means, the error in the value of the mean amplitude ratiocalculated can be greatly reduced, and thus the error in control ofreproducing power by the reproducing power control circuit 11 can begreatly reduced. Accordingly, with the present reproducing device,reproducing with an optimum light beam can be performed.

In addition, in the magneto-optical disk 1, the short mark recordingdomains 23 and long mark recording domains 24 are provided in eachsector 22. Further, when each sector 22 is reproduced, the drivingcurrent supplied to the semiconductor laser 12 is controlled so that thereproducing power of the semiconductor laser 12 is optimum for thatsector 22.

In this way, with the present reproducing device, reproducing powercontrol of the semiconductor laser 12 is performed with a short timeinterval. Accordingly, even if the environment in which the presentreproducing device is placed changes in a short time, causing theoptimum reproducing power of the semiconductor laser 12 to fluctuate ina short time, the reproducing power of the semiconductor laser 12 canalways be controlled to an optimum level. In other words, with thepresent reproducing device, control of the reproducing power of thesemiconductor laser 12 can respond to rapid fluctuations in the optimumreproducing power.

The following will explain the precision of control of the reproducingpower of the semiconductor laser 12 in the present reproducing device.This precision depends on the precision of the comparison resultoutputted by the differential amplifier 10, and this comparison result,in turn, depends on the precision of the mean amplitude ratio calculatedby the division circuit 9. Further, the precision of the mean amplituderatio (Ts_(mean)−Bs_(mean))/(Tl_(mean)−Bl_(mean)) depends on the meannumber of bytes of short marks and of long marks.

As mentioned above, the error correcting circuit 14 of the presentreproducing device is capable of correcting errors with certainty whenthe bit error rate (BER) of the binarized data received from the datareproducing circuit 8 is 1E-4 (1×10⁻⁴) or less. In other words, it ispreferable if the BER of the binarized data received from the datareproducing circuit 8 is within this range.

Further, in order to keep the BER of the binarized data within thisrange, it is preferable if the size of the aperture formed on themagneto-optical disk 1 by the present reproducing device is alwayswithin a predetermined size range. Further, at a constant ambienttemperature, the size of the aperture corresponds with the reproducingpower. Accordingly, it can be said that, at a constant ambienttemperature, there is a reproducing power range capable of keeping thesize of the aperture within a predetermined range.

Further, control of reproducing power by the Age reproducing powercontrol circuit 11 is performed in such a way that the reproducing poweris at an optimum level, but, as mentioned above, this control is basedon the comparison result outputted by the differential amplifier 10.This comparison result includes an error of a size corresponding to anerror included in the mean amplitude ratio calculated by the divisioncircuit 9. Accordingly, the control performed by the reproducing powercontrol circuit 11 includes an error equivalent to the error in thecomparison result of the differential amplifier 10.

Accordingly, it is preferable if the error of the comparison resultoutputted by the differential amplifier 10 is within a range whichensures that the reproducing power produced by the reproducing powercontrol circuit 11 is within the preferable reproducing power rangementioned above.

The comparison result of the differential amplifier 10 is obtained fromthe standard value and the mean amplitude ratio. Further, the standardvalue is the value of a previously detected mean amplitude ratio.Accordingly, it can be said that the error in the comparison result ofthe differential amplifier 10 is double the error of the mean amplituderatio outputted by the division circuit 9.

Accordingly, if the error in the mean amplitude ratio outputted by thedivision circuit 9 is no more than one-half of the allowable range oferror in the comparison result of the differential amplifier 10, the BERof the binarized data outputted by the data reproducing circuit 8 can beheld to 1E-4 or less. Furthermore, the range of error of the meanamplitude ratio corresponds with the mean number of bytes of short marksand of long marks in the short mark recording domain 23 and the longmark recording domain 24, respectively. In light of this fact, thefollowing will explain the range of error in the mean amplitude ratioand the preferable mean number of bytes of short marks and of longmarks.

FIG. 11 is a graph showing the results of measurement of therelationship between a mean number of bytes K of short marks and of longmarks in the magneto-optical disk 1 and the precision of the meanamplitude ratio detected by the present reproducing device.

As mentioned above, the short and long marks measured here were recordedby means of (1,7)RLL modulation. Further, in the Figure, precision ofthe mean amplitude ratio is shown as a standard deviation. This standarddeviation was obtained from the distribution of the results of detectionof mean amplitude ratio 100 times (the results of 100 reproductions ofsectors 22), and the size of the standard deviation corresponds to thesize of the distribution, i.e., the precision of the detected meanamplitude ratios.

FIG. 12 is a graph showing the results of measurement of therelationship between reproducing power of the semiconductor laser 12 andthe BER of the binarized data obtained from the data reproducing circuit8, and of the relationship between reproducing power and the meanamplitude ratio calculated by the division circuit 9. These measurementswere made at a constant ambient temperature.

As FIG. 12 shows, the reproducing power at which the BER is 1E-4 or lessis approximately 2.10 mW to 2.68 mW. In other words, the preferablereproducing power range at this ambient temperature is approximately2.10 mW to 2.68 mW. Further, when the reproducing power is within thisrange, the mean amplitude ratio is within a range from 0.14 through0.28. In other words, the mean amplitude ratio is 0.21±0.07, and thestandard value inputted to the differential amplifier 10 is 0.21.

Accordingly, at this ambient temperature, the reproducing power controlcircuit 11 controls the reproducing power so that the mean amplituderatios approach 0.21. Thus it can be seen that the allowable range oferror in control performed by the reproducing power control circuit 11,i.e., the allowable range of error in the comparison result of thedifferential amplifier 10, is ±0.07. Accordingly, it can be seen thatthe allowable range of error in the mean amplitude ratio outputted bythe division circuit 9 is ±0.035 (±0.07/2) or less.

Incidentally, the ranges of allowable error in the comparison result ofthe differential amplifier 10 and the mean amplitude ratio of thedivision circuit 9 change little even if the ambient temperaturechanges. The reasons for this will be explained below.

The measured results shown in FIG. 12 vary according to ambienttemperature. In other words, when the ambient temperature rises, themean amplitude ratio with respect to reproducing power shifts, inprinciple, in the direction of low power. Further, in such a case, theBER with respect to reproducing power also shifts in the direction oflow power. Accordingly, change in ambient temperature results in almostno change in the range of the mean amplitude ratio needed to keep theBER within the range of 1E-4 or less. In addition, change in thestandard deviation of the mean amplitude ratio (shown in FIG. 11)resulting from change in ambient temperature is, at reproducing powersnecessary to keep the BER within the foregoing range, small enough to beignored. This also holds true for measurements of a magneto-optical diskusing NRZI modulation, to be discussed below.

Accordingly, the ranges of allowable error in the comparison result ofthe differential amplifier 10 and the mean amplitude ratio of thedivision circuit 9 can be treated as ranges not dependent upon ambienttemperature.

According to statistics, when σ is the standard deviation of the meanamplitude ratio distribution (which can substantially be considered anormal distribution), if 3σ is 0.035 or less, the error in the meanamplitude ratio has better than a 99.7% probability of falling within±0.035. Accordingly, in order for the error in detecting the meanamplitude ratio to be within ±0.035, it can be seen that it ispreferable if a is 0.0117 (0.035/3) or less. Further, from FIG. 11, itcan be seen that the standard deviation is 0.0117 or less when the meannumber of bytes K is 5 bytes or more. Accordingly, it can be said thatit is preferable if the mean number of bytes K of short marks and oflong marks is 5 bytes or more.

Further, as shown by FIG. 11, if the mean number of bytes K is 40 bytesor more, there is almost no variation in the standard deviation.Consequently, a mean number of bytes K of 40 bytes or less issufficient.

The following will discuss the error in detecting the mean amplituderatio with a magneto-optical disk using NRZI modulation. Thismagneto-optical disk has the structure of the magneto-optical disk 1,except that a pattern of repeated short marks 2Tc in length, with aninterval between marks of 1Tc, is recorded in the short mark recordingdomain 23, and a pattern of repeated long marks 8Tc in length, with aninterval between marks of 8Tc, is recorded in the long mark recordingdomain 24.

FIG. 13 is a graph showing the results of measurement of therelationship between the mean number of bytes K′ of short marks and oflong marks and precision of the mean amplitude ratio detected by thepresent reproducing device. Here, as in FIG. 11, precision of the meanamplitude ratio is shown as a standard deviation. This standarddeviation was obtained from the distribution of the results of detectionof mean amplitude ratio 100 times. As shown in the Figure, if the meannumber of bytes K′ is 25 bytes or more, there is almost no variation inthe standard deviation.

FIG. 14 is a graph showing the results of measurement, when reproducingthis magneto-optical disk in the present reproducing device, of therelationship between reproducing power of the semiconductor laser 12 andthe BER of the binarized data obtained from the data reproducing circuit8, and of the relationship between reproducing power and the meanamplitude ratio calculated by the division circuit 9. These measurementswere made at a constant ambient temperature.

As FIG. 14 shows, with a reproducing power at which the BER is 1E-4 orless, the mean amplitude ratio is within a range from 0.23 through 0.38.In other words, at this ambient temperature, the mean amplitude ratio is0.305±0.075, and the standard value inputted to the differentialamplifier 10 is 0.305. Further, this range of ±0.075, for the reasonsexplained above, changes little according to ambient temperature.

Accordingly, in light of the same factors considered with themagneto-optical disk 1 recorded using (1,7)RLL modulation, it can beseen that it is preferable if the standard deviation a of the meanamplitude ratio distribution is 0.0125 (0.075/2/3) or less. Thus, it canbe seen from FIG. 13 that the average number of bytes K′ shouldpreferably be 5 bytes or more.

To summarize the foregoing results, it is preferable if the mean numberof bytes of the recorded marks for reproducing power control is at least5 bytes, and is sufficient if it is 40 bytes or less. In other words, itis preferable if the quantity of data recorded in each short markrecording domain 23 and long mark recording domain 24 is 5 bytes or moreand 40 bytes or less.

Accordingly, if 5 bytes or more and 40 bytes or less of recorded marksfor reproducing power control are recorded in the magneto-optical disk1, reproducing power control can be performed with sufficiently highprecision, and in a short time, without impairing the efficiency of useof the magneto-optical disk 1.

As shown in FIG. 15, with sampling of an analog reproducing signalcorresponding to short marks recorded using (1,7)RLL modulation, oneupper and one lower peak point are sampled for every four channel bits.Thus three amplitude value samples can be obtained per byte (12 channelbits). Again, as shown in FIG. 16, with sampling of an analogreproducing signal corresponding to long marks recorded using (1,7)RLLmodulation, four upper and four lower envelope points are sampled forevery 16 channel bits. Thus three amplitude value samples can beobtained per byte.

As shown in FIG. 17, with sampling of an analog reproducing signalcorresponding to short marks recorded using NRZI modulation, one upperand one lower peak point are sampled for every three channel bits. Thusapproximately 2.7 (=8/3) amplitude value samples can be obtained perbyte (8 channel bits). Again, as shown in FIG. 18, with sampling of ananalog reproducing signal corresponding to long marks recorded usingNRZI modulation, six upper and six lower envelope points are sampled forevery 16 channel bits. Thus three amplitude value samples can beobtained per byte.

Accordingly, with marks for reproducing power control recorded by(1,7)RLL modulation, it can be seen that if at least 15 samples aremade, the error in detecting the mean amplitude ratio will be within±0.035. Further, it can be seen that a number of samples of 120 or lessis sufficient.

Here, “number of samples” means the number of amplitude values used tocalculate the mean amplitude values.

Again, with marks for reproducing power control recorded by NRZImodulation, it can be seen that if at least (40/3), i.e., 14 samples aremade, the error in detecting the mean amplitude ratio will be within±0.035. Further, it can be seen that a number of samples of 120 or lessis sufficient.

Accordingly, it can be seen that, regardless of whether the modulationmethod of the magneto-optical disk is (1,7)RLL modulation or NRZImodulation, the number of short marks and of long marks should eachpreferably be 15 or more and 120 or less.

Incidentally, it was mentioned above that the error correcting circuit14 of the present reproducing device is capable of correcting errorswith certainty when the BER of the binarized data received from the datareproducing circuit 8 is 1E-4 or less. This correcting ability isequivalent to that of error correcting circuits used in typical opticalreproducing devices. In other words, a BER of 1E-4 or less is alsoconsidered preferable in conventional optical reproducing devices.

The preferable ranges of the mean numbers of bytes K and K′ and thenumber of samples of the recorded marks for reproducing power discussedabove may vary slightly depending on the reproducing characteristics ofthe optical reproducing device. However, reproducing characteristics ofoptical reproducing devices are not thought to vary so widely as to fallcompletely outside these ranges.

Further, in the present embodiment, the reproducing power of thesemiconductor laser 12 is controlled by a driving current, but inactuality, reproducing power also fluctuates according to ambienttemperature. However, in the present reproducing device, sincereproducing power is controlled so that the mean amplitude ratio isconstant, the reproducing power can be maintained at an optimum leveleven if the optimum level changes due to a change in ambienttemperature.

In order to compensate for fluctuations in reproducing power due tochanges in ambient temperature, a technology known as “APC” (Auto PowerControl) may also be used. By performing feedback of the differencebetween a previously set reproducing power and the current reproducingpower, this technology maintains the reproducing power at the setreproducing power even if the ambient temperature changes. In otherwords, the present reproducing device may be provided with a structurefor performing APC, and the foregoing set reproducing power may becontrolled by the reproducing power control circuit 11.

Again, the present reproducing device is structured so that the shortmark level detecting circuit 6 and the long mark level detecting circuit7 are provided with shift registers 31 and 41, respectively. Incalculating the mean amplitude values for the short marks and the longmarks, these means are calculated after inputting a predetermined numberof digital reproducing signal values into the shift registers 31 and 41,respectively. However, there is no need to be limited to the structureof the present reproducing device.

In other words, instead of storing in a shift register the digitalreproducing signal values for the upper and lower peak points inputtedto the short mark level detecting circuit 6, they each may becumulatively added, and when all of the respective values have beenadded, a short mark mean amplitude value may be found by dividing therespective sums by the number of samples, and then finding thedifference between the two divided values.

In the same way, instead of storing in a shift register the digitalreproducing signal values for the upper and lower peak points inputtedto the long mark level detecting circuit 7, they each may becumulatively added, and when all of the respective values have beenadded, a long mark mean amplitude value may be found by dividing therespective sums by the number of samples, and then finding thedifference between the two divided values.

Again, the short mark level detecting circuit 6 may be structured so asto extract from the digital reproducing signals corresponding to theshort marks only the sampling points at the upper and lower peaks of theanalog reproducing signal, find a mean thereof, and output this as theshort mark mean amplitude value. In the same way, the long mark leveldetecting circuit 7 may be structured so as to extract from the digitalreproducing signals corresponding to the long marks only the samplingpoints at the upper and lower peaks of the analog reproducing signal,find a mean thereof, and output this as the long mark mean amplitudevalue.

Again, the foregoing embodiment explains reproducing of amagneto-optical disk which uses the magnetic ultra high resolutionmethod, but memory media which can be reproduced by the presentreproducing device are not limited to this. The present reproducingdevice may also be structured so as to be able to reproducemagneto-optical disks which do not use the magnetic ultra highresolution method, optical disks, optical cards, optical tape, etc.

Again, the recording tracks 21 of the magneto-optical disk 1 areprovided in the form of concentric circles, but the magneto-optical disk1 may instead be provided with tracks in the form of a spiral.

In addition, the short marks and long marks of the magneto-optical disk1 need not be formed in advance in the short mark recording domain 23and the long mark recording domain 24. It is sufficient if themagneto-optical disk 1 is provided with domains of a predetermined size(for example, 5 bytes or more and 40 bytes or less) for forming of theshort marks and long marks. Then, prior to reproducing, the user'sdesired recorded marks for reproducing power control may be recorded inthese domains 23 and 24.

Further, in the present reproducing device, the short mark leveldetecting circuit 6 and the long mark level detecting circuit 7 performreproducing power control using upper and lower peak points in sampling,but the structure of the present reproducing device is not limited tothis. The short mark level detecting circuit 6 and the long mark leveldetecting circuit 7 may use any sampling points from which a short markmean amplitude value and a long mark mean amplitude value can becalculated.

In other words, the short mark level detecting circuit 6 and the longmark level detecting circuit 7 may extract, from the digital reproducingsignals corresponding to the short marks and long marks, the size of theanalog reproducing signal at a predetermined phase (for example, thesize at a phase corresponding to the shoulder of the analog reproducingsignal). Then, based on the extracted signal size, the short mark leveldetecting circuit 6 and the long mark level detecting circuit 7 maycalculate the short mark mean amplitude value and long mark meanamplitude value of this analog reproducing signal.

As discussed above, the device for controlling quantity of reproducinglight in the first optical reproducing device according to the presentinvention uses an optical memory medium from which data recorded in arecording layer is reproduced by forming on a reproducing layer anaperture smaller in diameter than the spot of a light beam projectedthereon, and includes control means which control reproducing power bydetecting a reproducing signal from marks for reproducing power controlrecorded in the optical memory medium; in which the control meanscontrol reproducing power on the basis of the reproducing signalobtained by reproducing 5 bytes or more and 40 bytes or less of themarks for reproducing power control.

Further, the device for controlling quantity of reproducing light in thesecond optical reproducing device according to the present inventionuses an optical memory medium from which data recorded in a recordinglayer is reproduced by forming on a reproducing layer an aperturesmaller in diameter than the spot of a light beam projected thereon, andincludes control means which control reproducing power by detecting areproducing signal from marks for reproducing power control recorded inthe optical memory medium; in which the control means controlreproducing power on the basis of the reproducing signal obtained byreproducing the marks for reproducing power control, making (40/3) ormore samples and 120 or more samples thereof.

Further, the device for controlling quantity of reproducing light in thethird optical reproducing device according to the present invention hasthe structure of the device for controlling quantity of reproducinglight in either the first or second optical reproducing device, furtherprovided with averaging means which average a plurality of amplitudevalues obtained by A/D conversion of the reproducing signal.

If the recording domains for the marks for reproducing power control aretoo large, the efficiency of use of the magneto-optical disk isimpaired. If these recording domains are too small, on the other hand,the distribution of the calculated mean amplitude ratios is increased,and the error in reproducing power control is increased.

With the foregoing structures of the devices for controlling quantity ofreproducing light in the first through third optical reproducingdevices, the recording domains for the marks for reproducing powercontrol are of a suitable size, and thus the efficiency of use of themagneto-optical disk can be increased, and sufficiently precise controlof reproducing power is possible.

Further, a first optical memory medium according to the presentinvention is an optical memory medium from which data recorded in arecording layer is reproduced by forming on a reproducing layer anaperture smaller in diameter than the spot of a light beam projectedthereon, in which are recorded 5 bytes or more and 40 bytes or less ofmarks for reproducing power control.

Further, a second optical memory medium according to the presentinvention has the structure of the first optical memory medium, in whichthe marks for reproducing power control are made up of a pattern ofrepeated short marks and a pattern of repeated long marks, and each ofthese patterns is 5 bytes or more and 40 bytes or less in quantity.

Further, a third optical memory medium according to the presentinvention has the structure of the first optical memory medium, in whichthe marks for reproducing power control are provided in each sector.

With the first through third optical memory mediums with the respectiveforegoing structures, it is possible to attain both efficient use of theoptical memory medium, by enlarging data recording domains, and precisereproducing power control. Further, by providing recording domains formarks for reproducing power control in each sector, reproducing powercan be controlled for each sector, and thus reproducing power controlcan respond with a short time interval. Accordingly, it becomes possibleto respond to rapid fluctuations in optimum reproducing power.

[Second Embodiment]

The second embodiment of the present invention will be explained below.

FIG. 19 is an explanatory drawing showing the structure of a magneticultra high resolution optical reproducing device (hereinafter referredto as “the present reproducing device”). As shown in the Figure, thepresent reproducing device is made up of an optical head 62, anidentification data reproducing circuit 64, a first clock producingcircuit 65, a second clock producing circuit 66, a clock selectingcircuit 67, an A/D converter 68, a PRML demodulating circuit 69, anamplitude ratio detecting circuit 70, a differential amplifier 71, and areproducing power control circuit 72. Further, the magneto-optical disk61 shown in FIG. 19 is an optical memory medium to be reproduced by thepresent reproducing device.

First, the structure of the magneto-optical disk 61 will be explained.The magneto-optical disk 61 is provided with a reproducing layer and arecording layer, and is a magnetic ultra high density magneto-opticalmemory medium from which digital data recorded in the recording layer isreproduced by forming on the reproducing layer an aperture smaller indiameter than a light beam spot projected thereon.

FIG. 20 is an explanatory drawing showing the structure of themagneto-optical disk 61. As shown in the Figure, a recording track 91 isformed in the shape of a circular band concentric with the circularmagneto-optical disk 61. Further, in the recording track 91 aresuccessively formed a plurality of sectors 92.

FIG. 21 is an explanatory drawing showing the structure of a sector 92.As shown in the Figure, in each sector 92 are formed a short markrecording domain 93, a long mark recording domain 94, a data recordingdomain 95, and an identification recording domain 96.

The short mark recording domains 93 (reproducing power control domains)are domains in which are formed short marks, which are marks forreproducing power control. The long mark recording domains 94(reproducing power control domains) are domains in which are formed longmarks, which are also marks for reproducing power control. The datarecording domains 95 are domains in which the user's desired data isrecorded as digital data. The modulation method for this digital datarecorded in the data recording domains 95 is not limited to anyparticular modulation method, but in what follows, it will be assumedthat digital data modulated by the (1,7)RLL (Run Length Limited)modulation method is recorded in the data recording domains 95.

FIG. 22 is an explanatory drawing showing the short marks and longmarks. As shown in the Figure, in the long mark recording domain 94,long marks having a mark length of 8Tc (Tc being the length of a channelbit) are successively formed at an interval of 8Tc. In the same way, inthe short mark recording domain 93, short marks having a mark length of2Tc are successively formed at a mark interval of 2Tc. In what follows,the number of short marks and long marks formed in the short markrecording domain 93 and the long mark recording domain 94 will be Nmarks and M marks, respectively (N and M being predetermined naturalnumbers).

The identification data recording domain 96 (disk information domain) isa domain in which are recorded in advance identification data foridentifying the modulation method of the digital data recorded in thedata recording domain 95 (hereinafter the “modulation methodidentification data”) and identification data for identifying the stateof recording of the recorded marks for reproducing power control, madeup of the short and long marks (hereinafter the “control markidentification data”). Here, the state of recording of the recordedmarks for reproducing power control means the sizes of the short markrecording domain 93 and the long mark recording domain 94, the marklengths and number of short and long marks recorded therein, thefrequency and phase of a clock signal suited to sampling of an analogreproducing signal corresponding to the short and long marks, etc.

The following will explain each of the structures of the presentreproducing device, shown in FIG. 19.

The optical head 62 (reproducing signal production section) includes asemiconductor laser 82 and a photodiode 83. The semiconductor laser 82(reproducing signal production section) projects a light beam a onto therecording track 91 of the magneto-optical disk 61 at a predeterminedreproducing power. The photodiode 83 (reproducing signal productionsection) receives light reflected from each of the domains 93 through 96of the sector 92 of the recording track 91, and produces and outputs ananalog reproducing signal corresponding to this reflected light. In whatfollows, this analog reproducing signal obtained from themagneto-optical disk 61 will be referred to as the “analog reproducingsignal c.”

The identification data reproducing circuit 64 (digital signal outputsection; clock signal selecting section; recorded mark judging section)receives the analog reproducing signal c produced by the photodiode 83,and obtains the modulation method identification data and the controlmark identification data from the analog reproducing signal ccorresponding to the identification data recording domain 96 of a singlesector 92. The identification data reproducing circuit 64 thenidentifies, from the two kinds of identification data, the type ofmodulation method and the characteristics of the recorded marks forreproducing power control, and sends these to the clock selectingcircuit 67. In what follows, the type of modulation method and thecharacteristics of the recorded marks for reproducing power control ofthe magneto-optical disk 61 identified and sent by the identificationdata reproducing circuit 64 will be referred to as the “diskinformation.”

The first clock producing circuit 65 (digital signal output section;clock signal producing section; first clock signal producing circuit)receives the analog reproducing signal c, and on the basis thereof, bymeans of PLL (Phase Locked Loop), produces and outputs a bit cycle clocksignal CLK1. In the same way, the second clock producing circuit 66(digital signal output section; clock signal producing section; secondclock signal producing circuit) receives the analog reproducing signalc, and on the basis thereof, by means of PLL (Phase Locked Loop),produces and outputs a bit cycle clock signal CLK2.

FIG. 23 is an explanatory drawing showing the clock signals CLK1 andCLK2. As shown in the Figure, the clock signal CLK1 and the clock signalCLK2 have the same frequency, but their phases differ by one-half cycle.In other words, the phase of the clock signal CLK2 is offset one-halfcycle (180°) with respect to the phase of CLK1.

The clock selecting circuit 67 (digital signal output section; clocksignal selecting section; clock signal selecting circuit) receives theclock signals CLK1 and CLK2, and the disk information of themagneto-optical disk 61 sent from the identification data reproducingcircuit 64. Then, on the basis of the disk information, the clockselecting circuit 67 selects one of the two clock signals and outputs itto the A/D converter 68.

The A/D converter 68 (digital signal output section; digital signalproducing section) receives the analog reproducing signal c and theclock signal sent from the clock selecting circuit 67. Then, on thebasis of the timing of the clock signal, the A/D converter 68 convertsthe analog reproducing signal c into digital reproducing signals, andoutputs these digital reproducing signals. In what follows, the digitalsignals outputted by the A/D converter 68 will be referred to as the“digital reproducing signals.”

The PRML demodulating circuit 69 (demodulation section) receives thedigital reproducing signals, and demodulates these digital reproducingsignals using the PRML (Partial Response Maximum Likelihood)demodulation method, thus producing binarized data.

The amplitude ratio detecting circuit 70 (reproducing power controlsection) receives the digital reproducing signals, and, based on thedigital reproducing signals corresponding to the short mark recordingdomain 93 and the long mark recording domain 94 of a single sector 92,calculates (detects) and outputs, by means of a method to be discussedbelow, a ratio between the amplitudes of the short and long marks(equivalent to reproducing signal quantity; hereinafter “mean amplituderatio”).

The differential amplifier 71 (reproducing power control section)compares the mean amplitude ratio received from the amplitude ratiodetecting circuit 70 with a standard value received from a standardvalue producing circuit (not shown), and outputs the result of thiscomparison (the difference of the mean amplitude ratio and the standardvalue).

The reproducing power control circuit 72 (reproducing power controlsection) supplies driving current to the semiconductor laser 82, and, bycontrolling the amperage of the driving current, controls thereproducing power of the semiconductor laser 82. The reproducing powercontrol circuit 72 receives the result of comparison from thedifferential amplifier 71, and controls the driving current supplied tothe semiconductor laser 82 so as to reduce the absolute value of thiscomparison result.

Next, selection of the clock signal by the clock selecting circuit 67will be explained.

On the basis of the disk information received from the identificationdata reproducing circuit 64, the clock selecting circuit 67 selects andoutputs to the A/D converter 68 the clock signal most suited to samplingof the analog reproducing signal c.

In other words, when the analog reproducing signal is a signalcorresponding to the digital data, the clock selecting circuit 67selects and outputs the clock signal most suited to sampling based onthe combination of the modulation method of the digital data and PRMLdemodulation in the PRML demodulating circuit 69.

Again, when the analog reproducing signal c is a signal corresponding torecorded marks for reproducing power control, the clock selectingcircuit 67 selects and outputs the clock signal most suited to samplingbased on the characteristics of the recorded marks, such as the marklengths of the short and long marks, the intervals therebetween, etc.

FIG. 24 is an explanatory drawing showing the relationship between theclock signals CLK1 and CLK2 and analog reproducing signals correspondingto the short marks and the long marks, which are sampled in accordancewith the clock signals. In other words, in FIG. 24, (a) shows samplingpoints when an analog reproducing signal c made up of short marks issampled based on the clock signal CLK1. Again, (b) shows sampling pointswhen an analog reproducing signal c made up of short marks is sampledbased on the clock signal CLK2. Again, (c) shows sampling points when ananalog reproducing signal c made up of long marks is sampled based onthe clock signal CLK1. In the Figure, sampling points of each analogreproducing signal, determined based on each clock signal, are shown by“∘.”

As shown in FIG. 24 at (a), the clock signal CLK1 has a phase suited todemodulating using PR(1,2,1)ML demodulation.

The pattern of recorded marks formed in the short mark recording domain93 is a pattern of repeated short marks 2Tc in length, as shown in FIG.22. For purposes of reproducing power control, it is preferable if theanalog reproducing signal c corresponding to these short marks issampled at upper and lower peak points.

Accordingly, as shown in FIG. 24 at (a), if the clock signal CLK1 isused, it is difficult to sample the upper and lower peak points of thisanalog reproducing signal c.

If, on the other hand, as shown in FIG. 24 at (b), the clock signal CLK2is used, it is easy to sample the upper and lower peak points of thisanalog reproducing signal c. Accordingly, sampling of an analogreproducing signal c corresponding to short marks should preferably beperformed based on the clock signal CLK2 rather than the clock signalCLK1.

Again, as shown in FIG. 22, the pattern of recorded marks formed in thelong mark recording domain 94 is a pattern of repeated long marks 8Tc inlength. For purposes of reproducing power control, it is preferable ifthe analog reproducing signal c corresponding to these long marks issampled at as many upper and lower envelope points as possible.Accordingly, as shown in FIG. 24 at (c), sampling of an analogreproducing signal c corresponding to long marks should preferably beperformed based on the clock signal CLK1 rather than the clock signalCLK2.

Accordingly, if the analog reproducing signal c is a signalcorresponding to digital data or to long marks, the clock selectingcircuit 67 outputs the clock signal CLK1 to the A/D converter 68. If theanalog reproducing signal c is a signal corresponding to short marks, onthe other hand, the clock selecting circuit 67 outputs the clock signalCLK2 to the A/D converter 68.

The following will explain the operations of the present reproducingdevice when reproducing the magneto-optical disk 61.

During reproducing, reproducing begins with the identification datarecording domain 96 of the sector 92 In other words, the light beam aprojected by the semiconductor laser 82 is first projected, at apredetermined initial reproducing power, onto the identification datarecording domain 96. This initial reproducing power is as follows. Whenthe reproducing power control circuit 72 is not receiving a feedbacksignal from the differential amplifier 71, the reproducing power controlcircuit 72 supplies a previously set initial driving current to thesemiconductor laser 82. In other words, the initial reproducing power ofthe semiconductor laser 82 is a reproducing power obtained in accordancewith the initial driving current.

When the light beam a from the semiconductor laser 82 is projected ontothe identification data recording domain 96 of the magneto-optical disk61, reflected light b reflected from the identification data recordingdomain 96 is received by the photodiode 83, which produces an analogreproducing signal c. This analog reproducing signal c is sent to theidentification data reproducing circuit 64, the first clock producingcircuit 65, the second clock producing circuit 66, and the A/D converter68.

Upon receiving the analog reproducing signal c, the identification datareproducing circuit 64 obtains, based on this signal, the modulationmethod identification data and the control mark identification data ofthe magneto-optical disk 61. The identification data reproducing circuit64 then identifies, from the two kinds of identification data, the typeof modulation method and the characteristics of the recorded marks forreproducing power control, and sends these, as the disk information, tothe clock selecting circuit 67.

In other words, the identification data reproducing circuit 64recognizes and informs the clock selecting circuit 67 that themodulation method of the digital data recorded in the data recordingdomain 95 of the magneto-optical disk 61 is (1,7)RLL modulation; that apattern of short marks 2Tc in length repeated at an interval of 2Tc isformed in the short mark recording domain 93; and that a pattern of longmarks 8Tc in length repeated at an interval of 8Tc is formed in the longmark recording domain 94.

After reproducing of the identification data recording domain 96, thelight beam a, still projected by the semiconductor laser 82 at thepredetermined initial reproducing power, is projected onto the shortmark recording domain 93 and the long mark recording domain 94. Then, aswith reproducing of the identification data recording domain 96, ananalog reproducing signal c corresponding to the short marks or the longmarks is produced and sent to the identification data reproducingcircuit 64, the first clock producing circuit 65, the second clockproducing circuit 66, and the A/D converter 68.

Upon receiving the analog reproducing signal c corresponding to theshort marks or the long marks, the first clock producing circuit 65produces and outputs to the clock selecting circuit 67 the clock signalCLK1 synchronized with the bit frequency of the analog reproducingsignal c. In the same way, the second clock producing circuit 66produces and outputs to the clock selecting circuit 67 the clock signalCLK2 synchronized with the bit frequency of the analog reproducingsignal c. As shown in FIG. 23, the phases of these two clock signals areoffset one-half cycle with respect to each other.

The clock selecting circuit 67, based on the disk information sent fromthe identification data reproducing circuit 64 at the time ofreproducing of the identification data recording domain 96, selects andoutputs to the A/D converter 68 one of the two clock signals CLK1 andCLK2.

The A/D converter 68 samples the analog reproducing signal c based onthe clock signal received from the clock selecting circuit 67, andproduces digital reproducing signals, which are sent to the PRMLdemodulating circuit 69 and the amplitude ratio detecting circuit 70.

After receiving digital reproducing signals corresponding to the shortmarks and the long marks, the amplitude ratio detecting circuit 70,based on these digital reproducing signals, calculates and outputs tothe differential amplifier 71 a mean amplitude ratio. Sampling of theanalog reproducing signals c corresponding to the long marks and theshort marks by the A/D converter 68, and calculation of the meanamplitude ratio by the amplitude ratio detecting circuit 70, will bediscussed later.

Upon receiving the mean amplitude ratio from the amplitude ratiodetecting circuit 70, the differential amplifier 71 compares the meanamplitude ratio with a standard value (an ideal value for the amplituderatio), and outputs the result of this comparison (the difference of themean amplitude ratio and the standard value) to the reproducing powercontrol circuit 72. The reproducing power control circuit 72 thencontrols the driving current supplied to the semiconductor laser 82 insuch a way that feedback reduces the absolute value of this comparisonresult. By this means, the semiconductor laser 82 projects the lightbeam a at an optimum reproducing power.

After the short mark recording domain 93 and the long mark recordingdomain 94 have been reproduced, the light beam a, now projected by thesemiconductor laser 82 at an optimum reproducing power, is projectedonto the data recording domain 95. Then, as with reproducing of theshort mark recording domain 93 and the long mark recording domain 94, ananalog reproducing signal c corresponding to the digital data is sent tothe first clock producing circuit 65, the second clock producing circuit66, and the A/D converter 68, and the clock signals CLK1 and CLK2 aresent to the clock selecting circuit 67.

Then, the clock selecting circuit 67, based on the disk information,outputs to the A/D converter 68 the clock signal CLK1, which is suitedto sampling of an analog reproducing signal c corresponding to digitaldata. The AID converter 68, based on the clock signal CLK1, samples theanalog reproducing signal c corresponding to the digital data, andproduces digital reproducing signals, which are sent to the PRMLdemodulating circuit 69 and the amplitude ratio detecting circuit 70.

In the PRML demodulating circuit 69, the digital reproducing signalscorresponding to the data recording domain 95 are equalized intoPR(1,2,1) characteristics, and decoded into the most likely data bymeans of Viterbi decoding, thus producing binarized data. The PRMLdemodulating circuit then outputs this binarized data to a binarizeddata processing device (not shown).

When reproducing of the data recording domain 95 is completed, thuscompleting reproducing of a single sector 92, another sector 92 adjacentthereto is reproduced in the same way.

The following will explain calculation of the mean amplitude ratio bythe amplitude ratio detecting circuit 70. In FIG. 25, (a) shows samplingby the A/D converter 68 of an analog reproducing signal c correspondingto short marks, and (b) shows sampling of an analog reproducing signal ccorresponding to long marks.

As shown in FIG. 25 at (a), on the basis of the clock signal CLK2, theA/D converter 68 samples the analog reproducing signal c correspondingto short marks at an upper peak point (Ts_(i)), an intermediate point(shown in the Figure as “x”), a lower peak point (Bs_(i)), and anintermediate point (i being a natural number). The digital reproducingsignals obtained by sampling are sent in order to the amplitudedetecting circuit 70.

Then, the amplitude detecting circuit 70 calculates from the digitalreproducing signal values obtained from a predetermined number ofsamples of Ts_(i) a mean value Ts_(mean) (a mean value for the upperpeak points). In other words, the amplitude detecting circuit 70calculates the mean value Ts_(mean) by finding the sum of the digitalreproducing signal values obtained from a predetermined number ofsamples of Ts_(i), and then dividing the sum by that predeterminednumber.

Next, in the same way, the amplitude detecting circuit 70 calculatesfrom the digital reproducing signal values obtained from a predeterminednumber of samples of Bs_(i) a mean value Bs_(mean) (a mean value for thelower peak points). Here, the number of samples of Ts_(i) and of Bs_(i)used in calculating the mean values Ts_(mean) and Bs_(mean) are equal.The amplitude detecting circuit 70 then calculates the differencebetween these two mean values (Ts_(mean)−Bs_(mean)), and treats thisvalue as the mean amplitude value for the short marks.

Again, as shown in FIG. 25 at (b), on the basis of the clock signalCLK1, the A/D converter 68 samples the analog reproducing signal ccorresponding to long marks at four upper envelope points (Tl_(j+1),Tl_(j+2), Tl_(j+3), and Tl_(j+4)), four intermediate points (shown inthe Figure as “x”), four lower envelope points (Bl_(j+1), Bl_(j+2),Bl_(j+3), and Bl_(j+4)), and four intermediate points (j being amultiple of 4). The digital reproducing signals obtained by sampling aresent in order to the amplitude detecting circuit 70.

Then, the amplitude detecting circuit 70 calculates from the digitalreproducing signal values obtained from a predetermined number ofsamples of Tl_(j+k) (with k=1 to 4) a mean value Tl_(mean) (a mean valuefor the upper envelope points). In other words, the amplitude detectingcircuit 70 calculates the mean value Tl_(mean) by finding the sum of thedigital reproducing signal values obtained from a predetermined numberof samples of Tl_(j+k), and then dividing the sum by that predeterminednumber.

Next, in the same way, the amplitude detecting circuit 70 calculatesfrom the digital reproducing signal values obtained from a predeterminednumber of samples of Bl_(i+k) (with k=1 to 4) a mean value Bl_(mean) (amean value for the lower envelope points). Here, the number of samplesof Tl_(j+k) and of Bl_(j+k) used in calculating the mean valuesTl_(mean) and Bl_(mean) are equal. The amplitude detecting circuit 70then calculates the difference between these two mean values(Tl_(mean)−Bl_(mean)), and treats this value as the mean amplitude valuefor the long marks.

Then the amplitude ratio detecting circuit 70 calculates a ratio betweenthe mean amplitude values for the short marks and the long marks(Ts_(mean)−Bs_(mean))/(Tl_(mean)−Bl_(mean)) as the mean amplitude ratio.

As discussed above, the magneto-optical disk 61 to be reproduced by thepresent reproducing device is provided with identification datarecording domains 96, in which are recorded in advance the modulationmethod identification data and the control mark identification data.

Then the identification data reproducing circuit 64 of the presentreproducing device obtains the modulation method identification data andthe control mark identification data, identifies the modulation methodof the digital data and the characteristics of the recorded marks forreproducing power control, and sends these to the clock selectingcircuit 67 as the disk information. Further, the clock selecting circuit67 also receives clock signals CLK1 and CLK2, which are clock signals ofdifferent phase.

Then, based on the disk information, the clock selecting circuit 67outputs to the A/D converter 68 either the clock signal CLK1 or theclock signal CLK2. In other words, the clock selecting circuit 67selects and outputs to the A/D converter the clock signal most suited toA/D conversion of the analog reproducing signal c, based on the typethereof.

Accordingly, the sampling performed by the A/D converter 68 is performedat a sampling frequency suited to the analog reproducing signal cinputted. In other words, analog reproducing signals c corresponding tothe digital data and to the recorded marks for reproducing power controlare sampled at an optimum phase, as shown in FIG. 24 at (a) through (c).

By this means, the PRML demodulating circuit 69 is enabled to performgood PRML demodulating. Accordingly, with the present reproducingdevice, the magneto-optical disk 61 recorded by PRML modulation can bereproduced with a low error rate.

Again, in the same way, the amplitude ratio detecting circuit 70 is ableto correctly detect the peak values or envelope values of analogreproducing signals c corresponding to the recorded marks forreproducing power control, and to calculate a mean amplitude ratio (thereproducing signal quantity). Accordingly, with the present reproducingdevice, it is possible to accurately control the reproducing power ofthe semiconductor laser 82, i.e., the quantity of light of thesemiconductor laser 82.

In this way, with the present reproducing device, even if the optimumclock signal for reproducing the digital data (which is determined bythe combination of the modulation method of the digital data and thedemodulation method) differs from the optimum clock signal forreproducing the recorded marks for reproducing power control (which isdetermined by the type of recorded marks for reproducing power control),all of the digital data and recorded marks for reproducing power controlcan be reproduced based on an optimum clock signal.

Again, with the present reproducing device, a single A/D converter 68sends digital reproducing signals to both the amplitude ratio detectingcircuit 70 and the PRML demodulating circuit 69. In other words, asingle A/D converter sends digital reproducing signals to circuits whichperform two different kinds of processing. Accordingly, the presentreproducing device can be realized by means of a simple structure.

Further, in the present reproducing device, reproducing power control ofthe semiconductor laser 82 is performed each time reproducing of asector is begun. Accordingly, reproducing power control is performed atshort time intervals. Accordingly, even if the environment in which thepresent reproducing device is placed changes in a short time, causingthe optimum reproducing power of the semiconductor laser 82 to fluctuatein a short time, the reproducing power of the semiconductor laser 82 canalways be controlled to an optimum level. In other words, with thepresent reproducing device, control of the reproducing power of thesemiconductor laser 82 can respond to rapid fluctuations in the optimumreproducing power.

The following will discuss the reasons why the sampling of the shortmarks by the clock signal CLK1 shown in FIG. 24 at (a) is suited todemodulation using the PR(1,2,1)ML demodulation method.

With the PR(1,2,l)ML demodulation method, a better error rate can beobtained the closer a solitary wave-form (1Tc) is to PR(1,2,1)characteristics. These PR(1,2,1) characteristics are characteristics inwhich, as shown in FIG. 33, level ratios for samplings at each channellock cycle are . . . , 0, 1, 2, 1, 0, . . . Further, since a reproducingsignal corresponding to a pattern of repeated recorded marks 2Tc inlength is a superimposition of these solitary wave-forms, it has awave-form like that shown in FIG. 34. Accordingly, when sampling areproducing signal corresponding to this pattern, a clock signal whichsamples points at the shoulder of the reproducing signal, as shown inFIG. 24 at (a), is optimum.

In the present embodiment, the modulation method of the digital data inthe magneto-optical disk 61 is (1,7)RLL modulation, and the method ofPRML demodulation by the PRML demodulating circuit 69 is PR(1,2,1)MLdemodulation. However, the digital data modulation method able to bereproduced by the present reproducing device is not limited to (1,7)RLLmodulation, and any modulation method may be used. Further, the methodof demodulation by the PRML demodulating circuit 69 is not limited toPR(1,2,1)ML demodulation, and any type of PRML demodulation may be used.

Again, in the present embodiment, the data recorded in theidentification data recording domains 96 of the magneto-optical disk 61is of two types, modulation method identification data and control markidentification data, but the recorded data is not limited to these. Thedata recorded in the identification data recording domains 96 and sentto the clock selecting circuit 67 may also be data such as thefollowing.

When the magneto-optical disk 61 records several types of digitalinformation (including the digital data and the recorded marks forreproducing power control), and the clock signal most suited toreproducing the digital information differs according to the type ofdigital information, the identification data recording domains 96 mayrecord data specifying the clock signal most suited to reproducing ofeach type of digital information, the location of each type of digitalinformation in each sector, etc. If this type of magneto-optical disk 61is used, the present reproducing device is enabled to performreproducing of each type of digital information on the basis of anoptimum clock signal.

Further, in the present embodiment, the magneto-optical disk 61 isprovided with identification data recording domains 96, in which arerecorded the modulation method identification data and the control markidentification data. Then the identification data reproducing circuit 64of the present reproducing device obtains the modulation methodidentification data and the control mark identification data, and, basedon this identification data, sends the disk information to the clockselecting circuit 67. However, the structure of the present reproducingdevice and of the magneto-optical disk 61 need not be limited to therespective structures discussed above.

In other words, the present reproducing device may be structured so thatthe analog reproducing signal c is sent to the clock selecting circuit67, which identifies the type of the analog reproducing signal c byanalyzing With this structure, the clock selecting circuit 67 outputsone of the two clock signals to the A/D converter 68 on the basis of theidentified type of the analog reproducing signal c. Further, with thisstructure, the magneto-optical disk 61 need not be provided with theidentification data recording domains 96.

Again, in the present reproducing device, the phases of the clocksignals CLK1 and CLK2 are offset by one-half cycle, but the clocksignals to be sent to the clock selecting circuit 67 need not be limitedto these. In other words, it is satisfactory if the clock signals sentto the clock selecting circuit 67 are optimum for reproducing of thedigital data and recorded marks for reproducing power control recordedin the magneto-optical disk 61.

Again, in the present embodiment, the short marks recorded in themagneto-optical disk 61 are marks which are best reproduced using theclock signal CLK2, and the long marks are marks which are bestreproduced using the clock signal CLK1, but the recorded marks forreproducing power control recorded in the magneto-optical disk 61 arenot limited to these.

For example, the long marks may be marks which are best reproduced bythe clock signal CLK2. In other words, both the long marks and shortmarks for reproducing power control may be marks which are bestreproduced using the clock signal CLK2.

When reproducing a magneto-optical disk 61 with this kind of structure,the first clock producing circuit 65 of the present reproducing deviceis a circuit for producing the clock signal for reproducing of thedigital data, and the second clock producing circuit 66 is a circuit forproducing the clock signal for reproducing of the recorded marks forreproducing power control.

With this structure, even if, for example, the first clock producingcircuit 65 is unable to output a normal clock signal CLK1 due tounlocking of the PLL, etc., this will have no influence on reproducingpower control by the amplitude ratio detecting circuit 70, thedifferential amplifier 71, and the reproducing power control circuit 72.Accordingly, even in the event of malfunctions in the first clockproducing circuit 65, normal reproducing power control can be continued.

Again, in the present reproducing device, the clock signals sent to theclock selecting circuit 67 are of two types, CLK1 and CLK2, but thenumber of clock signals sent to the clock selecting circuit 67 is notlimited to two.

As many clock signals as necessary in optimum reproducing of the digitaldata and the recorded marks for reproducing power control may be sent tothe clock selecting circuit 67.

Again, in the present embodiment, the magneto-optical disk 61 has astructure in which the identification data recording domain 96 isprovided as a separate domain in the sector 92. However, theidentification data recording domain 96 may be provided within the shortmark recording domain 93, within the long mark recording domain 94, orwithin another domain. Again, instead of providing an identificationdata recording domain 96 for each sector 92, one identification datarecording domain 96 may be provided for each recording track 91, or foreach magneto-optical disk 61.

In addition, the magneto-optical disk 61 may be a conventional magneticultra high resolution optical memory medium provided with a reproducinglayer and a recording layer, from which data recorded in the recordinglayer is reproduced by forming on the reproducing layer an aperturesmaller in diameter than the light spot of the semiconductor laser 82.

Further, the PRML demodulating circuit 69 of the present reproducingdevice may have a structure equivalent to that of the conventional PRMLdemodulating circuit 26.

Again, the present reproducing device may have a structure in which,prior to reproducing of the digital data or the recorded marks forreproducing power control, the identification data reproducing circuit64 reproduces the modulation method identification data and the controlmark identification data recorded in the identification data recordingdomain 96, and recognizes in advance that the modulation method of thedigital data is (1,7)RLL modulation, and that the recorded marks forreproducing power control are made up of a pattern of repeated shortmarks 2Tc in length and a pattern of repeated long marks 8Tc in length.

In addition, in the present reproducing device, the amplitude ratiodetecting circuit 70 calculates the mean amplitude ratio, but thestructure of the present reproducing device is not limited to this. Forexample, instead of the amplitude ratio detecting circuit 70, thepresent reproducing device may be provided with the short mark leveldetecting circuit 6, the long mark level detecting circuit 7, and thedivision circuit 9 described in the first embodiment above.

Further, the short marks, long marks, and disk information of themagneto-optical disk 61 need not be formed in advance in the short markrecording domain 93, the long mark recording domain 94, and theidentification data recording domain 96. It is sufficient if themagneto-optical disk 61 is provided with domains of a predetermined sizefor forming of the short marks, long marks, and disk information. Then,prior to reproducing, the user's desired recorded marks for reproducingpower control and disk information may be recorded in these domains 93,94, and 96.

[Third Embodiment]

The following will explain the third embodiment of the presentinvention. Members having functions equivalent to those of the secondembodiment above will be given the same reference symbols, andexplanation thereof will be omitted.

FIG. 26 is an explanatory drawing showing the structure of an opticalreproducing device according to the present embodiment (hereinafter the“present reproducing device”). As shown in the Figure, instead of theidentification data reproducing circuit 64, the first clock producingcircuit 65, the second clock producing circuit 66, the clock selectingcircuit 67, the A/D converter 68, and the amplitude ratio detectingcircuit 70 of the optical reproducing device according to the secondembodiment above, the present reproducing device is provided with adoubled clock producing circuit 101, an A/D converter 102, a signalseparating circuit 103, a long/short mark extracting circuit 104, and anamplitude ratio detecting circuit 105.

Further, the magneto-optical disk 100 shown in FIG. 26 is an opticalmemory medium to be reproduced by the present reproducing device. Themagneto-optical disk 100 is not provided with the short mark recordingdomain 93, the long mark recording domain 94, and the identificationdata recording domain 96 of the magneto-optical disk 61 according to thesecond embodiment above. In other words, the recorded marks forreproducing power control, made up of the short and long marks, are notrecorded in the magneto-optical disk 100, in which only the user'sdesired data is recorded as digital data.

Based on the analog reproducing signal c received from the photodiode83, the doubled clock producing circuit 101 (digital signal outputsection; clock signal output section) produces and outputs a clocksignal CLK3 with a frequency double the bit frequency (the reproducingbit frequency).

FIG. 27 is an explanatory drawing comparing the clock signal CLK3 withthe clock signals CLK1 and CLK2 shown in FIG. 23. As shown in FIG. 27,the clock signal CLK3 is a clock signal with a frequency double that ofthe clock signals CLK1 and CLK2. Accordingly, the clock signal CLK3 is aclock signal which includes both a phase suited to PR(1,2,1)MLdemodulation and to detecting of upper and lower envelope points of thelong marks shown in FIG. 22, and a phase suited to detecting of upperand lower peak points of the short marks shown in FIG. 22.

On the basis of the timing of the clock signal CLK3, the A/D converter102 (digital signal output section; digital signal producing section)converts the analog reproducing signal c into digital reproducingsignals, and outputs these digital reproducing signals. In what follows,the digital signals outputted by the A/D converter 102 will be referredto as the “digital reproducing signals.”

The signal separating circuit 103 (digital signal output section;digital signal separating section) receives the digital reproducingsignals, and, based on the timing of the clock signal CLK3, assigns eachdigital reproducing signal value alternately to one of two signals, andoutputs these two signals.

The long/short mark extracting circuit 104 (reproducing power controlsection; timing detecting section) receives binarized data from the PRMLdemodulating circuit 69, and extracts therefrom only binarized datacorresponding to recorded marks 2Tc in length and recorded marks 8Tc inlength.

The following will explain the operations of the present reproducingdevice when reproducing the magneto-optical disk 100. The operationsthrough producing of an analog reproducing signal c from themagneto-optical disk 100 are equivalent to those of the opticalreproducing device according to the second embodiment above, andexplanation thereof will be omitted.

In the present reproducing device, the analog reproducing signal coutputted by the photodiode 83 is sent to the doubled clock producingcircuit 101 and the A/D converter 102. As mentioned above, since thereare no recorded marks for reproducing power control recorded in themagneto-optical disk 100, the analog reproducing signal c outputted bythe photodiode 83 is always one corresponding to digital data.

Based on the analog reproducing signal c inputted thereto, the doubledclock producing circuit 101 produces a clock signal CLK3 having afrequency double the bit frequency of the analog reproducing signal c,and outputs the clock signal CLK3 to the AID converter 102 and thesignal separating circuit 103. The A/D converter 102 samples the analogreproducing signal c based on the clock signal CLK3, thus producingdigital reproducing signals, which are sent to the signal separatingcircuit 103.

FIG. 28 is an explanatory drawing explaining the production of digitalreproducing signals by the A/D converter 102 when it receives an analogreproducing signal c corresponding to recorded marks 2Tc in length(equivalent to the short marks). In the Figure, “∘” and “●” indicate thepoints sampled by the A/D converter 102 based on the clock signal CLK3.

As shown in the Figure, the A/D converter 102, based on the clock signalCLK3, alternately samples sampling points shown by “∘,” which are suitedto PRML detecting (and to recorded marks 8Tc in length) and samplingpoints shown by “●,” which are suited to detecting a peak value ofrecorded marks 2Tc in length.

Next, FIG. 29 is an explanatory drawing explaining the production ofdigital reproducing signals by the A/D converter 102 when it receives ananalog reproducing signal c corresponding to digital data which is arandom pattern of recorded marks of various lengths. In this Figure,too, the points sampled by the A/D converter 102 are shown by “∘” and“●.”

By means of this kind of sampling, the A/D converter 102 producesdigital reproducing signals, which are sent to the signal separatingcircuit 103.

The signal separating circuit 103 assigns each inputted digitalreproducing signal alternately to one of two groups of signals. In otherwords, the signal separating circuit 103 separates the digitalreproducing signals shown by “∘” in FIG. 29 (hereinafter collectivelyreferred to as the “first digital reproducing signal”) from the digitalreproducing signals shown by “●” (hereinafter collectively referred toas the “second digital reproducing signal”). The signal separatingcircuit 103 then sends the first digital reproducing signal to the PRMLdemodulating circuit 69, and sends both the first digital reproducingsignal and the second digital reproducing signal to the amplitude ratiodetecting circuit 105.

Upon receiving the first digital reproducing signal, the PRMLdemodulating circuit 69 equalizes this signal into PR(1,2,1)characteristics, and then decodes it into the most likely data by meansof Viterbi decoding, thus producing binarized data. The PRMLdemodulating circuit 69 then sends this binarized data to the long/shortmark extracting circuit 104 and to a binarized data processing device(not shown).

The binarized data sent to the long/short mark extracting circuit 104corresponds to recorded marks of seven different lengths from 2Tc to8Tc. The long/short mark extracting circuit 104 extracts from thebinarized data the data obtained from recorded marks 8Tc in length, anddetermines the times at which the samplings which obtained this datawere performed (hereinafter referred to as the “first sampling times”).The long/short mark extracting circuit 104 also, in the same way,extracts from the binarized data the data obtained from recorded marks2Tc in length, and determines the times at which the samplings whichobtained this data were performed (hereinafter referred to as the“second sampling times”). The long/short mark extracting circuit 104then sends a predetermined number of first sampling times and apredetermined number of second sampling times to the amplituderatio-detecting circuit 105.

The amplitude ratio detecting circuit 105 (reproducing power controlsection; reproducing power control circuit), based on the first samplingtimes received from the long/short mark extracting circuit 104,calculates from the first digital reproducing signal a mean amplitudevalue for the recorded marks 8Tc in length, i.e., the mean amplitudevalue (Tl_(mean)−Bl_(mean)) for the long marks discussed in the secondembodiment above. The amplitude ratio detecting circuit 105 also, basedon the second sampling times received from the long/short markextracting circuit 104, calculates from the second digital reproducingsignal a mean amplitude value for the recorded marks 2Tc in length,i.e., the mean amplitude value (Ts_(mean)−Bs_(mean)) for the short marksdiscussed in the second embodiment above.

The amplitude ratio detecting circuit 105 then calculates a ratiobetween these two mean amplitude values, i.e., the mean amplitude ratio(Ts_(mean)−Bs_(mean)/(Tl) _(mean)−Bs_(mean)) discussed in the secondembodiment above, and sends this ratio to the differential amplifier 71.

Calculation of the mean amplitude values and the mean amplitude ratio bythe amplitude ratio detecting circuit 105 is performed by the samecalculation method as in the amplitude ratio detecting circuit 70 in thesecond embodiment above. Further, control of the reproducing power ofthe semiconductor laser 82 by the differential amplifier 71 and thereproducing power control circuit 72 is performed as in the secondembodiment above.

As discussed above, in the present reproducing device, the doubled clockproducing circuit 101 produces a clock signal CLK3 having a frequencydouble that of the clock signals CLK1 and CLK2, and the A/D converter102 produces digital reproducing signals by performing sampling based onthis clock signal CLK3. Then the signal separating circuit 103 assignseach digital reproducing signal alternately to one of two digitalreproducing signals, which are sent to the amplitude ratio detectingcircuit 105 and the PRML demodulating circuit 69. Then the long/shortmark extracting circuit 104 identifies the sampling times of therecorded marks (equivalent to the short and long marks), and sends thesesampling times to the amplitude ratio detecting circuit 105, whichcalculates a mean amplitude ratio.

Accordingly, with the present reproducing device, a mean amplitude ratiocan be calculated, and the reproducing power of the semiconductor laser82 controlled, even when reproducing a memory medium which, like themagneto-optical disk 100, is not provided with recording domains forreproducing power control (such as the identification data recordingdomains 96, short mark recording domains 93, and long mark recordingdomains 94 of the second embodiment above).

Accordingly, using the present reproducing device, it is possible toreproduce a magneto-optical disk whose efficiency of use, i.e., theproportion of the disk allotted to the data recording domains 95, ishigher than that of the magneto-optical disk 61 discussed in the secondembodiment above.

In the present embodiment, the modulation method of the digital data inthe magneto-optical disk 100 is (1,7)RLL modulation, and the method ofPRML demodulation by the PRML demodulating circuit 69 is PR(1,2,1)MLdemodulation. However, the digital data modulation method able to bereproduced by the present reproducing device is not limited to (1,7)RLLmodulation, and any modulation method may be used. Further, the methodof demodulation by the PRML demodulating circuit 69 is not limited toPR(1,2,1)ML demodulation, and any type of PRML demodulation may be used.

In other words, it is sufficient if the doubled clock producing circuit101 is able to produce a single clock signal corresponding to theoptimum clock signal for reproducing the digital data (which isdetermined by the combination of the modulation method of the digitaldata and the demodulation method) and the optimum clock signal forreproducing the recorded marks for reproducing power control (which isdetermined by the type of recorded marks for reproducing power control).

Again, the foregoing embodiment explained reproducing of amagneto-optical disk which uses the magnetic ultra high resolutionmethod, but memory media which can be reproduced by the presentreproducing device are not limited to this. The present reproducingdevice may also be structured so as to be able to reproducemagneto-optical disks which do not use the magnetic ultra highresolution method, optical disks, optical cards, optical tape, etc.

Again, the long/short mark extracting circuit 104 may also be structuredso as to extract from the binarized data received from the PRMLdemodulating circuit 69 only the recorded marks 2Tc and 8Tc in length,and to send to the amplitude ratio detecting circuit 105 the samplingpoints at the times of extraction of each type of mark.

Again, since the sampling phase which is most suited to the reproducingsignal of the recorded marks for reproducing power control differsaccording to the combination of the modulation method of the digitaldata, the PRML demodulation method, and the types of recorded marks forreproducing power control, the present reproducing device may be given astructure which is optimum for the reproducing system used.

As discussed above, a fourth optical reproducing device according to thepresent invention controls the light quantity of a light beam based on areproducing signal obtained by projecting the light beam onto an opticalmemory medium in which recorded data and recorded marks are recorded,and is made up of clock producing means, which produce a first samplingclock and a second sampling clock of a phase differing from that of thefirst sampling clock, for sampling of the reproducing signal; A/Dconversion means, which A/D convert the reproducing signal; PRMLdemodulating means, which demodulate the recorded data which has beenA/D converted in accordance with the first sampling clock; signalquantity detecting means, which detect reproducing signal quantity fromthe recorded marks which have been A/D converted in accordance with thesecond sampling clock; and light quantity control means, which controlthe light quantity of the light beam based on the reproducing signalquantity.

With this fourth optical reproducing device, by selecting an optimumsampling phase for A/D conversion according to whether PRML demodulationis being performed or recorded marks for reproducing power control arebeing detected, a low error rate can be obtained in reproducing data byPRML detecting, and a reproducing signal quantity can be calculated bycorrectly detecting peak values of the reproducing signal of therecorded marks for reproducing power control. Thus accurate control ofreproducing power can be realized.

Further, a fifth optical reproducing device according to the presentinvention is structured as the fourth optical reproducing device above,in which the clock producing means are separately provided with firstPLL means, for producing the first sampling clock, and second PLL means,for producing the second sampling clock.

With this fifth optical reproducing device, by means of a structurewhich separately provides a PLL for producing the sampling clock forPRML demodulation and a PLL for producing the sampling clock fordetecting the amplitude value of the recorded marks for reproducingpower control, even if the PLL for PRML demodulation is unable to outputa normal clock due to unlocking, etc., this will not influence detectingof the recorded marks for reproducing power control, and thus normalcontrol of reproducing power can be continued.

Further, a sixth optical reproducing device according to the presentinvention is structured as the fourth optical reproducing device above,and further includes clock selecting means, which switch to the firstsampling clock when performing PRML demodulation and to the secondsampling clock when performing light quantity control, and which outputthe selected sampling clock to the A/D conversion means.

With this sixth optical reproducing device, by changing the samplingtiming for A/D conversion by switching between the two clocks ofdifferent phase, a single A/D converter can be used both for PRMLdemodulation and for detecting recorded marks for reproducing powercontrol. Thus the structure of the reproducing device can bestreamlined.

Further, a seventh optical reproducing device according to the presentinvention is structured as the sixth optical reproducing device above,and further includes identification data reproducing means forreproducing identification data for identifying the clock needed in PRMLdemodulation and the clock needed in light quantity control; in whichthe clock selecting means are switched based on the identification data.

Further, a fourth optical memory medium according to the presentinvention is an optical memory medium provided with a reproducing layerand a recording layer, from which data recorded in the recording layeris reproduced by forming on the reproducing layer an aperture smaller indiameter than the spot of a light beam projected thereon, and isprovided with identification data recording domains in which arerecorded identification data for identifying a difference in phasebetween a clock for detecting reproducing signal quantity, which is usedfor controlling the light quantity of the light beam, and a clock forreproducing data.

With the seventh optical reproducing device and the fourth opticalmemory medium, identification data regarding the modulation method, thetypes of recorded marks for reproducing power control, etc. is recordedin identification data recording domains in the magneto-optical disk,and the clock for A/D conversion is selected on the basis of theidentification data distinguished by the identification data reproducingmeans. This structure enables setting of an optimum sampling phase forA/D conversion of recording marks for reproducing power control, whichcan vary according to the combination of the PRML method, the modulationmethod of the recorded data, and the types of recorded marks forreproducing power control. Thus accurate control of reproducing powercan be realized.

Further, an eighth optical reproducing device according to the presentinvention controls the light quantity of a light beam based on areproducing signal obtained by projecting the light beam onto an opticalmemory medium in which recorded data and recorded marks are recorded,and is made up of doubled clock producing means, which produce asampling clock with a frequency double that of a reproducing clock ofthe reproducing signal; A/D converting means, which A/D convert thereproducing signal using the sampling clock; separating means, whichassign the A/D converted output signals during each sampling clockalternately to one of two signals, and output these two signals; PRMLdemodulating means, which receive and demodulate one of the two signalsseparated by the separating means; signal quantity detecting means,which receive and detect a reproducing signal quantity from the other ofthe two signals separated by the separating means; and light quantitycontrol means, which control the light quantity of the light beam basedon the reproducing signal quantity.

With the eighth optical reproducing device, by means of a structure inwhich, using a sampling clock having a frequency double the reproducingbit frequency, A/D converted reproducing signals during each samplingclock are alternately assigned to one of two signals, amplitude valuesof shortest marks and longest marks can be detected from among therecorded data, which includes marks of various lengths. Consequently,recorded marks for reproducing power control are unnecessary, and theefficiency of use of the magneto-optical disk can be increased.

Further, a ninth optical reproducing device according to the presentinvention is made up of a reproducing signal production section, whichprojects a light beam onto an optical memory medium, and, based onreflected light of the light beam, produces a reproducing signalcorresponding to recorded marks recorded in the optical memory medium; acontrol signal output section, which detects a mean value of a signalquantity of the reproducing signal produced by the reproducing signalproduction section, and produces a first control signal corresponding tothe mean value; and a reproducing power control section, which, based onthe first control signal produced by the control signal output section,controls reproducing power of the light beam projected by thereproducing signal production section such that the signal quantity ofthe reproducing signal is an optimum value.

Further, a tenth optical reproducing device according to the presentinvention is structured as the ninth optical reproducing device above,in which the control signal output section is made up of a peak valuedetecting section, which detects a predetermined number of maximal andminimal values of a reproducing signal corresponding to the recordedmarks of the optical memory medium; a mean value producing section,which, from the predetermined number of maximal and minimal valuesdetected by the peak value detecting section, produces a mean value ofthe amplitude value of the reproducing signal; and a control signalproducing section, which, based on the mean value produced by the meanvalue producing section, produces a first control signal.

Further, an eleventh optical reproducing device according to the presentinvention is structured as the tenth optical reproducing device above,in which the peak value detecting section detects a predeterminedquantity of maximal and minimal values of a reproducing signalcorresponding to first recorded marks of a predetermined mark length,and a predetermined quantity of maximal and minimal values of areproducing signal corresponding to second recorded marks of a marklength differing from that of the first recorded marks; and the meanvalue producing section is made up of a first mean value calculatingsection, which, based on the maximal and minimal values of thereproducing signal corresponding to the first recorded marks, calculatesa mean value of an amplitude thereof, and a second mean valuecalculating section, which, based on the maximal and minimal values ofthe reproducing signal corresponding to the second recorded marks,calculates a mean value of an amplitude thereof; and the control signalproducing section produces the first control signal by finding a ratiobetween the mean value calculated by the first mean value calculatingsection and the mean value calculated by the second mean valuecalculating section.

Further, a twelfth optical reproducing device according to the presentinvention is structured as the eleventh optical reproducing deviceabove, in which each of the first and second mean value calculatingsections, includes a shift register for storing the predeterminedquantity of maximal and minimal values of the reproducing signalcorresponding to the first or second recorded marks detected by the peakvalue detecting section; a first addition circuit for calculating a sumof all of the maximal values stored in the shift register; a secondaddition circuit for calculating a sum of all of the minimal valuesstored in the shift register; a first division circuit for calculating amean value for the maximal values by dividing the sum of the maximalvalues calculated by the first addition circuit by the predeterminedquantity; a second division circuit for calculating a mean value for theminimal values by dividing the sum of the minimal values calculated bythe second addition circuit by the predetermined quantity; and a firstsubtraction circuit for calculating a mean value of the amplitude of thereproducing signal corresponding to the first recorded marks or to thesecond recorded marks by subtracting the mean value for the minimalvalues calculated by the second division circuit from the mean value forthe maximal values calculated by the first division circuit.

Further, a thirteenth optical reproducing device according to thepresent invention is structured as the ninth optical reproducing deviceabove, in which the reproducing power control section is made up of adifferential amplifier, to which is inputted the first control signaland a predetermined standard value, and which produces a second controlsignal which is a result of comparison between the first control signaland the standard value; and a reproducing power adjusting section, whichcontrols the reproducing power such that the value of the second controlsignal is reduced; and the second control signal is produced such that aBER of the reproducing signal produced by the reproducing signalproduction section is 1E-4 or less.

Further, a fifth optical memory medium according to the presentinvention is made up of a recording layer for recording data, and areproducing layer, laminated on the recording layer, on which anaperture is formed by projection of a predetermined light beam, fromwhich aperture the data recorded on the recording layer is read; inwhich the recording layer includes data recording domains in which areformed recorded marks for recording of ordinary data, and reproducingpower control domains, in which are formed 5 bytes or more and 40 bytesor less of recorded marks for reproducing power control, for controllingreproducing power of the light beam.

Further, a sixth optical memory medium according to the presentinvention is structured as the fifth optical memory medium above, inwhich each reproducing power control domain includes a domain in whichare formed 5 bytes or more and 40 bytes or less of first recorded marksof a predetermined mark length; and a domain in which are formed 5 bytesor more and 40 bytes or less of second recorded marks of a mark lengthdiffering from that of the first recorded marks.

Further, a seventh optical memory medium according to the presentinvention is structured as the fifth optical memory medium above, inwhich the reproducing power control domains are provided in each sectorformed on the recording layer.

Further, an eighth optical memory medium according to the presentinvention is made up of a recording layer for recording data, and areproducing layer, laminated on the recording layer, on which anaperture is formed by projection of a predetermined light beam, fromwhich aperture the data recorded on said recording layer is read; inwhich the recording layer includes a data recording domain, in which areformed recorded marks for recording of ordinary data, a reproducingpower control domain, in which are formed recorded marks for reproducingpower control, for controlling reproducing power of the light beam, anda disk information domain, in which are recorded the modulation methodof the recorded marks in the data recording domain and the reproducingpower control domain, and the state of recording of the recorded marksfor reproducing power control.

The embodiments and concrete examples of implementation discussed in theforegoing detailed explanation of the present invention serve solely toillustrate the technical contents of the present invention, which shouldnot be narrowly interpreted within the limits of such concrete examples,but rather may be applied in many variations without departing from thespirit of the present invention and the scope of the patent claims setforth below.

1. An optical memory medium comprising a recording layer for recordingdata, and a reproducing layer, laminated on said recording layer, onwhich an aperture is formed by projection of a predetermined light beam,from which aperture the data recorded on said recording layer is read,wherein: a track for recording of data includes a reproducing powercontrol domain of 5 bytes or more and 40 bytes or less, for recording ofrecorded marks for reproducing power control, for controllingreproducing power of the light beam.
 2. The optical memory medium setforth in claim 1, wherein said reproducing power control domainincludes: a domain of 5 bytes or more and 40 bytes or less, forrecording of first recorded marks of a predetermined mark length; and adomain of 5 bytes or more and 40 bytes or less, for recording of secondrecorded marks of a mark length differing from that of the firstrecorded marks.
 3. The optical memory medium set forth in claim 1,wherein: a said reproducing power control domain is provided in eachsector formed on said track.
 4. An optical memory medium comprising arecording layer for recording data, and a reproducing layer, laminatedon said recording layer, on which an aperture is formed by projection ofa predetermined light beam, from which aperture the data recorded onsaid recording layer is read, wherein: on a track for recording of dataare provided: a data recording domain, for recording of ordinary data; areproducing power control domain, for recording of recorded marks forreproducing power control, for controlling reproducing power of thelight beam; and a disk information domain, for recording of themodulation method of the recorded marks in said data recording domainand said reproducing power control domain, and the state of recording ofthe recorded marks for reproducing power control.